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323 Cards in this Set

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  • Back
How does the textbook define forensic science?
Forensic science is the application of science to criminal and civil laws that are enforced by police agencies in a criminal justice system.
Why is Mathieu Orfila considered “the father of forensic toxicology"?
Orfila published the first scientific treatise on the detection of poisons and their effects on animals.
What was Francis Galton’s principal contribution to forensic science?
Galton undertook the first definitive study of fingerprints and developed a methodology of classifying them for filing.
How did Calvin Goddard advance the science of firearms examination?
Goddard was the first to use a comparison microscope to analyze bullets to determine whether they were fired from the same gun.
What is Locard’s exchange principle?
Locard’s exchange principle states that whenever two objects come into contact with one another, there is exchange of materials between them. When this happens during the commission of a crime, the cross-transfer of evidence can connect the suspect to his or her victim.
What major advance in forensic science did the state of California undertake in 1972?
In 1972 California began creating an integrated network of state-operated forensic laboratories consisting of regional and satellite facilities.
How does the British system of forensic laboratories differ from that of the United States?
In contrast to the American system of independent local laboratories, Britain has developed a national system of regional laboratories under the direction of the government’s Home Office.
How has the emergence of the “fee-for-service” system affected the practice of forensic science in Great Britain?
The fee-for-service concept has encouraged the creation of a number of private laboratories that make their services available to police and defense alike.
List three reasons for the unparalleled growth of crime laboratories in the United
States since the 1960's.
1. Supreme Court decisions in the 1960s required police to place greater emphasis on securing scientifically evaluated evidence and all but eliminated confessions as a routine investigative tool.
2. The dramatic increase in U.S. crime rates led to a greater need for scientific examination of criminal evidence.
3. The advent of DNA profiling led to a need for crime labs to expand their staffs and modernize their facilities to meet the demands of DNA technology.
Describe how the structure of the U.S. federal government has affected the organization of crime labs in the United States.
The federal system of government emphasizes the importance of retaining local control over important matters such as criminal prosecution. This has led to the growth of many local and state crime laboratories and precluded the creation of a national system. In addition, the federal government has no single law enforcement or investigative agency that has unlimited jurisdiction throughout the country.
List three main reasons for the wide variation in total services offered by crime labs in different communities.
1. Variations in local laws
2. Different capabilities and functions of the organization to which a laboratory is attached
3. Budgetary and staffing limitations.
Describe the basic duties of the physical science unit in a crime lab and give three
examples of the type of work performed by a physical science unit.
The physical science unit applies principles and techniques of chemistry, physics, and geology to the identification and comparison of crime-scene evidence. Three examples of the type of work performed by the physical science unit are drug identification, soil and mineral analysis, and examination of trace physical evidence.
In addition to the physical science unit, what four units typically are found in full service crime labs? List at least one function performed by each of these units.
Biology unit - Performs DNA testing, hair/fiber comparison and botanical material comparison
Firearms unit - Examines firearms, ammunition, clothing and evidence
Document examination unit - Ascertains authenticity of documents and recovers lost data
Photography unit - Examines and records physical evidence using specialized techniques to render invisible information
List two optional units found in most crime labs and give at least one example of the type of work done by each.
Toxicology unit - Examines body fluids and organs to determine the presence or absence of foreign substances
Latent fingerprint unit - Processes and examines evidence for latent fingerprints.
List the main functions of the forensic scientist.
Analyzing physical evidence;
Providing expert testimony
Furnishing training in the proper recognition, collection,
and preservation of physical evidence.
What important principle was established in the case of Frye v. United States?
The principle that questioned procedures, techniques, or principles must be “generally accepted” by a meaningful segment of the relevant scientific community before
they are admissible as evidence at trial.
How did the court’s ruling in the case of Daubert v. Merrell Dow Pharmaceuticals, Inc. affect the admissibility of scientific evidence in federal courts?
In Daubert v. Merrell Dow Pharmaceuticals, Inc., the Supreme Court asserted that “general acceptance” is not an absolute prerequisite to the admissibility of scientific evidence under the Federal Rules of Evidence. According to the Court, the Rules of Evidence assign to the trial judge the task of ensuring that an expert’s testimony rests on a reliable foundation and is relevant to the task at hand.
How does the testimony of an expert witness differ from the testimony of a lay witness?
A lay witness must give testimony on events or observations that arise from personal knowledge. This testimony must be factual and, with few exceptions, cannot contain the personal opinions of the witness. By contrast, the expert witness evaluates evidence that the court lacks the expertise to do, and thus must express his or her personal opinion as to the significance of the findings. The views expressed are accepted only as representing the expert’s opinion and may later be accepted or ignored in jury deliberations.
List two ways in which a forensic odontologist can assist in criminal investigations.
Forensic odontologists can use dental records such as X-rays, dental casts, and a photograph of a person’s smile to compare a set of dental remains and a suspected victim. A forensic odontologist can also compare bite marks left on a victim to the tooth structure of suspects.
How does the textbook define physical evidence?
Physical evidence is any object that can establish that a crime has been committed or can link a crime and its victim or a crime and its perpetrator.
What is the first critical step in crime-scene investigation? Why is this step so important?
The first critical step in crime-scene investigation is securing and isolating the crime scene. It is critical because anyone who enters a crime scene potentially could destroy physical evidence important to the investigation.
List the three methods of crime-scene recording.
The three methods of crime-scene recording are photography, sketches, and notes.
What is the most important prerequisite for photographing a crime scene? Why is this so critical?
The most important prerequisite for photographing a crime scene is for the scene to be in an unaltered condition. If objects at the scene have been removed, been added, or changed positions, the photographs may not be admissible as evidence at a trial, and their intended value will be lost.
What is a rough sketch and what information must it accurately reflect?
A rough sketch is a draft representation of all essential information and measurements at a crime scene. A rough sketch must accurately depict the dimensions of the crime scene as well as all recovered items of physical evidence and their exact locations.
What information must be included in any notes taken at the crime scene?
Crime-scene notes must include a detailed written description of the scene with the location of items of physical evidence recovered. They must also identify the time at which an item of physical evidence was discovered, by whom, how and by whom it was packaged and marked, and the disposition of the item after it was collected.
Besides the crime scene itself, what locations must investigators search?
The areas searched must include all probable points of entry and exit used by the criminal(s).
What items from deceased victims must be collected and sent to a forensic laboratory?
The following items must be sent to the forensic laboratory: the victim’s clothing, fingernail scrapings, head and pubic hairs, blood, bullets recovered from the body, hand swabs (from shooting victims), and vaginal/anal/oral swabs (in sex-related crimes).
What is the main objective in collecting and packaging physical evidence?
The main objective in collecting and packaging physical evidence is to prevent any change in the evidence between the time it is removed from the crime scene and the time it is received by the crime laboratory.
What is the best way to maintain the integrity of evidence that is collected and submitted to the crime laboratory?
The integrity of evidence is best maintained when the item is kept in its original condition as found at the crime site.
Why is it important to package items of physical evidence in separate containers?
Packaging evidence separately prevents damage through contact and cross contamination.
Why should ordinary mailing envelopes not be used for packaging physical evidence?
Ordinary mailing envelopes should not be used as evidence containers because powders and fine particles will leak out of their corners.
Describe a druggist fold and explain why it is a superior way to package small amounts of trace evidence.
A druggist fold consists of folding one end of a piece of paper over one-third, then folding the other end (one-third) over that, and repeating the process from the other two sides. After the paper is folded in this manner, the outside two edges are tucked into each other. A druggist fold produces a closed container that keeps the specimen from falling out.
Why should bloodstained evidence not be stored in airtight containers? What is the best way to store such evidence?
Bloodstained materials should not be stored in airtight containers because the accumulation of moisture in such containers may encourage the growth of mold, which can destroy the evidential value of blood. In these instances, wrapping paper, manila envelopes, and paper bags are recommended packaging materials.
Define chain of custody and explain why maintaining a proper chain of custody is important.
The chain of custody is a list of all people who came into possession of an item of evidence. Maintaining a proper chain of custody is the best guarantee that the evidence will withstand inquiries of what happened to it from the time of its finding to its presentation in court.
What are the possible consequences of failing to maintain a proper chain of custody?
Failure to substantiate the evidence’s chain of custody may lead to serious questions regarding the authenticity and integrity of the evidence and examinations of it.
What is a standard/reference sample and why is it important to the criminalist?
A standard/reference sample is physical evidence whose origin is known, such as blood or hair from a suspect that can be compared to crime-scene evidence. Standard/reference samples are important because they allow the criminalist to connect evidence found at the scene of a crime to the suspect and/or victim.
What is a substrate control and why is it important?
A substrate control consists of uncontaminated surface material close to an area where physical evidence has been deposited. A substrate control ensures that the surface on which a sample has been deposited does not interfere with the interpretation of laboratory tests.
Why is it important to include a brief description of the case history on an evidence submission form?
Providing a case history allows the examiner to analyze specimens in a logical sequence and make the proper comparisons, and it also facilitates the search for trace quantities of evidence.
What two diseases have sensitized the law enforcement community to the potential health hazards that can exist at crime scenes?
The spread of AIDS and hepatitis B have sensitized the law enforcement community to the potential health hazards that can exist at crime scenes.
Name three basic types of protective clothing that investigators use to guard against contamination by infectious materials at a crime scene.
Three basic types of protective clothing recommended for investigators are latex gloves, shoe covers, and liquid-repellent coveralls.
List four situations in which a warrantless search may be justified.
1. The existence of emergency circumstances,
2. The need to prevent the immediate loss or destruction of evidence,
3. A search of a person and property within the immediate control of the person provided it is made incident to a lawful arrest
4. A search made by consent of the parties involved.
List six types of physical evidence derived from human or other animal sources that commonly are found at crime scenes.
blood, semen, saliva, hair, fingerprints, organs, and physiological fluids
List and define the two methods used by forensic scientists when examining physical evidence.
Identification - The process of determining a substances
physical or chemical identity.
Comparison - The process of ascertaining whether two or
more objects have a common origin.
To permit positive identification, testing procedures used by a forensic scientist must meet what two conditions?
Testing procedures must give characteristic results
for specific standard materials as well as the number and type of tests required to positively identify a substance must be sufficient to exclude all other substances.
Describe the two steps in the process of comparison. What question does each step attempt to answer?
The first step in comparison is determining which properties from the suspect and standard/reference specimen to compare. This step attempts to determine whether the two samples are the same. The second step is concluding the origins of the specimens. This step attempts to determine how likely it is that two samples came from the same source.
Define individual and class characteristics.
Individuals characteristics - Properties of evidence that can be attributed to a common source with an extremely high degree of certainty.
Class characteristics - Properties of evidence that can be associated only with a group and never with a single source.
Define the product rule and explain how it can be used to determine whether two blood samples come from the same source.
The product rule states that one can obtain an overall frequency of occurrence for a genetic profile by multiplying together the frequencies of independently occurring genetic markers. If several different factors from two blood samples are found to be identical, a forensic scientist can apply the product rule to calculate how frequently blood containing that combination of factors occurs in the population. The more blood factors that match,the greater the probability that the two blood samples originated from a common source.
What is the greatest weakness of class evidence? List two factors that contribute to this weakness.
The greatest weakness of class evidence is that examiners cannot assign exact or even approximate probability values to the comparison of most class evidence. Few statistical data exist from which to derive comparative information for most class evidence, and society is increasingly dependent on mass-produced products that are extremely difficult to distinguish from one another.
What is the value of class evidence? Why is this important in making a case to a jury?
The value of class evidence lies in its ability to corroborate events with data that are, as nearly as possible, free of human error and bias. This is important because most other types of evidence (such as eyewitness testimony and confessions) are subjective in nature and susceptible to dispute, human error, or bias.
Why are some jurists wary of allowing unconditional use of scientific evidence in court?
Some jurists are wary about scientific evidence because juries often accord scientific evidence greater weight than other evidence, tend to consider it more trustworthy, and often view it with less skepticism. Without proper safeguards, the use of scientific evidence may unfairly prejudice a case against the accused.
How can the extreme sensitivity of modern analytical techniques hinder the process of comparing items of physical evidence?
When measured or examined with extreme precision, no two items—even those originating from the same source—are exactly alike. Thus, using an analytic technique that is too sensitive makes it impossible to meaningfully compare different items of evidence.
What are IAFIS and CODIS? Describe the purpose of each.
IAFIS is the Integrated Automated Fingerprint Identification System, a national fingerprint and criminal history database maintained by the FBI. IAFIS allows criminal investigators to compare fingerprints at a crime scene to an index of 500 million known prints. CODIS is the FBI’s Combined DNA Index System. It enables federal, state, and local crime laboratories to electronically exchange and compare DNA profiles, linking crimes to each other and to convicted offenders.
List and describe three physical and/or chemical changes that occur in the body that enable a forensic pathologist to determine time of death.
Rigor Mortis - Stiffening of the muscles. Occurs within 24 hours of death and disappears within 36 hours.
Livor Mortis - The settling of blood in the parts of the body closest to the ground. Creates a dark blue or purple appearance immediately and continues for up to 12 hours after death.
Algor Mortis - The cooling of the body after death. Occurs at a predictable rate, enabling the pathologist to estimate time of death from the temperature of the body.
What important considerations must be made when determining PMI using forensic entomology?
The time required for stage development is affected by environmental influences such as geographical location, climate, weather conditions, and the presence of drugs.
List the areas of the skeleton that can be used to determine the gender of skeletal remains.
The gender can be determined by observing the shape of the pelvis and sacrum, the size of the cranium, and the protrusion of the brow bone and mastoid process.
Define the terms physical property and chemical property.
A physical property is the behavior of a substance without alteration of the substance’s composition through a chemical reaction. A chemical property is the behavior of a substance when it reacts or combines with another substance.
Why is the metric system of measurement easier to use than the “English system”?
The metric system is easier to use because it employs a simple decimal relationship so that any unit of length, volume, or mass can be converted into another unit by multiplying or dividing by a factor of 10. By contrast, no simple numerical relationship exists between the various units of measurement in the English system.
Which measuring system is used in the United States?
The English system is used in the United States.
List the basic units of length, mass, and volume in the metric system.
The basic units of length, mass, and volume in the metric system are the meter, the gram, and the liter, respectively.
What reference points are most often chosen when constructing a temperature scale?
The most convenient reference points are the melting point of ice and the boiling point of water.
List the two most commonly used temperature scales and their respective reference points.
The most commonly used temperature scales are the Fahrenheit and Celsius scales. The Fahrenheit scale uses a melting point of 32° and a boiling point of 212°. The Celsius scale uses a melting point of 0° and a boiling point of 100°.
Define weight and mass and explain the difference between the two concepts.
Weight is a property of matter that depends on both the mass of a substance and the effects of gravity on that mass. Mass is a constant property of matter that reflects the amount of material present. Because weight depends on the force of gravity, the weight of an object can vary from one location to another. Mass differs from weight because it remains the same regardless of location.
What is density?
Density is a physical property of matter that is equivalent to the mass per unit volume of a substance.
How does heat affect the density of gases and liquids?
As the temperature of a liquid or gas increases, its density decreases.
Define the terms refraction and refractive index.
Refraction is the bending of a light wave as it passes from one medium to another. Refractive index is the ratio of the speed of light in a vacuum to its speed in a given substance.
What is the difference between a crystalline solid and an amorphous solid? How does this difference affect the refractive index of each of these types of solid?
The atoms in a crystalline solid have a regular arrangement; the atoms in an amorphous solid have no regular order. Amorphous solids have only one refractive index; crystalline solids have two refractive indices.
Explain how a prism disperses white light into its constituent colors.
Because each color component of light has a slightly different frequency, each color passes through the prism at a slightly different speed. This causes each color component to refract at a different angle as it emerges from the prism, thus dispersing the light into its constituent colors.
Define intensive property and name two intensive properties of matter.
An intensive property is a property that is not dependent on the size of an object. Intensive properties include density and refractive index.
List two factors that make it difficult for criminalists to compare glass samples.
Most glass evidence presented to the criminalist is either too fragmentary or too minute for the pieces to be physically reassembled or fitted together. In addition, the general chemical composition of various window glasses has so far been found to be relatively uniform among various manufacturers and thus offers no basis for identifying individual samples
Describe the process of flotation and explain what it is used for.
Flotation is a process used to compare the densities of glass samples. In flotation, a standard/reference glass particle is immersed in a liquid. The composition of the liquid is carefully adjusted until the glass remains suspended in the liquid. Glass chips of approximately the same size and shape as the standard/reference are then added to the liquid for comparison. If both the unknown and the standard/reference particles remain suspended in the liquid, their densities are equal to each other and to that of the liquid.
What is the Becke line and how is it used to determine the refractive index of a glass sample?
The Becke line is a bright halo observed near the border of a particle that is immersed in a liquid with a different refractive index. When the refractive index of the liquid is altered so that it is the same as that of the glass sample immersed in it, the Becke line disappears. This reveals the refractive index of the sample.
What is the 3R rule and how is it applied to the analysis of glass fractures?
The 3R rule states that Radial cracks form a Right angle on the Reverse side of the force. This rule enables an examiner to determine readily the side on which a window or pane of glass was broken.
How can an investigator determine the order in which several successive penetrations of a glass occurred?
It is frequently possible to determine the sequence of impacts in glass by observing the existing fracture lines and their points of termination. Each fracture always terminates at an existing line of fracture.
How can soil evidence be valuable even if the site of the crime has not been ascertained?
A geologist may be able to examine soil found on a victim or suspect and direct police to an area or areas where the soil originally may have been picked up. This can make it easier for the police to determine where the crime was committed.
What is a mineral and how can minerals be important in the comparison of soil samples?
A mineral is a naturally occurring crystalline solid that can be identified by its physical properties. The combination of minerals found in different soil or rock samples can be used to compare the samples to determine whether they have the same origin.
What is the most important consideration when collecting soil samples from a crime scene?
Establishing the variation of soil at the crime scene is the primary consideration when collecting soil specimens.
At what locations should soil standard/reference samples be collected?
Standard/reference soil samples should be collected at the site of the crime, at various intervals within a 100-yard radius of the crime scene, and at all possible alibi locations that the suspect may claim.
Why is soil collected from suspect automobiles left in lump form?
Soil is collected as lumps because lumps preserve a record of the buildup of several of layers of soil from different locations over time. This layering effect gives a sample greater variation, and thus makes it easier to compare the sample to soil samples found at the site of an accident.
Define the terms element and compound and name the smallest unit of each.
An element is a fundamental particle of matter. A compound is a pure substance composed of two or more elements. The smallest unit of an element is an atom. The smallest unit of a compound is a molecule
Name the three forms, or states, of matter and explain how the shape and volume of matter are expressed in each state.
The three states of matter are solid, liquid, and gas. A solid has both a specific shape and volume. A liquid has a specific volume, but takes the shape of the container in which it resides. A gas has neither a specific shape nor a specific volume.
What physical change occurs when a substance undergoes the following changes of state: (a) from liquid to solid, and (b) from liquid to gas?
When a substance undergoes a change of state from liquid to solid, the attractive forces between the molecules increase in strength. When a substance undergoes a change of state from liquid to gas, the attractive forces between the molecules decrease in strength.
Define sublimation.
Sublimation is a physical change from the solid state directly into the gaseous state.
What happens to the attractive forces between molecules of a substance that undergo sublimation?
Sublimation causes the attractive forces between molecules to decrease in strength.
What is a phase and how can two different phases be distinguished from one another?
A phase is a uniform piece of matter. Different phases are distinguished from one another by definite visible boundaries.
What is the fundamental difference between organic and inorganic substances?
Organic substances are based on the element carbon; inorganic substances are not.
Describe the difference between a quantitative and a qualitative determination.
A qualitative determination simply identifies the material in question, whereas a quantitative determination defines the percentage combination of the various components of a mixture.
What basic tool is most often used to characterize and identify organic materials? Why is this tool chosen for that purpose?
Spectrophotometry is the basic tool used to characterize and identify organic materials. It is used because the nature of the forces or bonds that exist between the elements in organic compounds allow scientists to readily characterize organic compounds by their absorption of light.
What is the greatest drawback to spectrophotometry?
Spectrophotometry requires that a material be in a relatively pure state, but the purity of physical evidence is almost always beyond the control of the criminalist.
What technique is often employed when spectrophotometry cannot be used?
Chromatography is often employed when spectrophotometry cannot be used to analyze physical evidence.
Briefly describe the basic chromatographic process. Be sure to explain how motion is important to the process.
In one form of chromatography, a questioned mixture is dissolved in liquid so that some of its molecules enter the surrounding air as gas molecules, while others remain in the liquid. During this process, the air containing the gas molecules is forced to move continuously in one direction over the liquid. If one component of the mixture has a greater percentage of its molecules in the moving (gas) phase than other components, those molecules travel over the liquid at a faster pace. When the moving phase has advanced a reasonable distance, the molecules of the different components are completely separated from one another. This allows the scientist to identify the various components in the mixture
What three chromatographic processes are most applicable for solving analytical problems typically encountered in the crime laboratory? What is the main advantage of each?
Gas chromatography, high-performance liquid chromatography (HPLC), and thinlayer chromatography (TLC). Gas chromatography is widely used because of its ability to resolve a highly complex mixture into its components, usually within minutes. The major advantage of HPLC is that the entire process takes place at room temperature and so it can be used to analyze sensitive materials that may be destroyed at the high temperatures experienced during gas chromatography. TLC is inexpensive and allows numerous samples to be analyzed simultaneously on one thin-layer plate.
What is electrophoresis and what is it most widely used for?
Electrophoresis is a technique for the separation of molecules through their migration on a support medium while under the influence of an electrical potential. Electrophoresis is widely used in the characterization of proteins and DNA in dried blood.
What is color?
Color is a visual indication of the fact that objects absorb certain portions of visible light and transmit or reflect others.
What determines the color of an opaque object?
The color of an opaque object is determined by which component color(s) of light it reflects.
What two models do scientists use to explain the nature of light? Under what conditions does each model best describe the behavior of light?
The first model describes light as a continuous wave; the second depicts it as a stream of discrete energy particles. When light is moving through space, its behavior can best be described as that of a continuous wave. Light as a stream of discrete particles best describes its behavior when light is absorbed by a substance.
What is Beer’s law and what analytical technique is based on it?
Beer’s law states that the quantity of light absorbed at any frequency is directly proportional to the concentration of material absorbing it; the more material one has, the more radiation it will absorb. Beer’s law permits spectrophotometry to be used as a technique for quantification.
Briefly describe the basic process of spectrophotometry.
In spectrophotometry, a beam of radiation is passed through a tube containing an unknown sample dissolved in a solution. A detector then compares the intensity of radiation passing through the solution to the intensity of a similar beam of radiation that does not pass through the solution. A signal from the detector is then fed into a recorder that produces an absorption spectrum that characterizes the sample being tested.
What are the main strength and main weakness of ultraviolet spectrophotometry?
The main strength of UV spectrophotometry is that the spectra it produces are very simple, which makes determining a material’s probable identity easier. The main drawback of UV spectrophotometry is that UV spectra of different substances can be similar, so the technique may not provide a definitive result.
What major advantage does infrared spectrophotometry enjoy over ultraviolet spectrophotometry?
Because different materials always have distinctively different infrared spectra, the IR spectrum for each substance is unique. Thus, unlike UV spectrophotometry, IR spectrophotometry can reliably identify specific substances.
What is the most important drawback to gas chromatography?
The most important drawback of gas chromatography is that a forensic chemist cannot identify an unknown substance based solely on the results of gas chromatography.
In what area does mass spectrometry currently have its greatest application for forensic scientists?
At present, mass spectrometry finds its widest application in areas relating to the identification of drugs.
What is a trace element and why are trace elements important in analyzing physical evidence?
A trace element is an element found in very small quantities. For the criminalist, the presence of trace elements is particularly useful because they provide markers that may establish the source of a material or at least provide additional points for comparison of two items of physical evidence
Explain how the analysis of trace elements was important to the investigation of the assassination of President John F. Kennedy.
Bullets recovered from Kennedy’s brain, the wrist of Governor John Connally, and the car in which both were riding at the time of the assassination were found to have almost identical concentrations of the trace elements silver and antimony. This supports the conclusion that the bullets that struck Kennedy and Connally were fired by the same shooter.
What two characteristics of elements form the basis of the analytical techniques of emission spectroscopy and atomic absorption spectrophotometry?
Elements selectively absorb and emit light.
Describe the difference between a continuous spectrum and a line spectrum. Which is most helpful in identifying a particular element and why?
A continuous spectrum shows a continuous band of colors all blending into one another. A line spectrum shows a series of lines separated by black areas in which each line represents a definite wavelength or frequency. A line spectrum is most helpful in identifying a particular element because it serves as a unique “fingerprint” of an element that differs from the spectra of all other elements.
How does the quantity of light absorbed during atomic absorption spectrophotometry relate to the concentration of the absorbing element? What is the significance of this relationship for the forensic scientist?
The concentration of the absorbing element is directly proportional to the quantity of the light absorbed. This allows the forensic scientist to accurately determine the concentration of a particular element in a sample.
Why do forensic scientists often use inductively coupled plasma (ICP) emission spectrophotometry to analyze mutilated bullets?
Mutilated bullets are often not suitable for traditional microscopic comparisons against an exemplar test-fired bullet. In such situations, ICP emission spectrophotometry can be used to obtain an elemental profile of the questioned bullet fragment for comparison against an unfired bullet generally found in the possession of the suspect.
What is the main drawback to atomic absorption spectrophotometry?
The main drawback to atomic absorption spectrometry is that it allows the analyst to determine only one element in a sample at a time. The forensic scientist must thus run several tests using different lamps to identify all of the elements in a sample
What advantage does “flameless” atomic absorption enjoy over standard atomic absorption techniques?
“Flameless” atomic absorption spectrometry is substantially more sensitive, allowing the forensic scientist to detect many elements at levels that approach onetrillionth of a gram.
List the three basic subatomic particles and indicate whether each has positive, negative, or no electrical charge.
Proton - Positive
Neutron - Neutral
Electron - Negative
What is the net electrical charge of an atom? What does this indicate about the arrangement of subatomic particles in an atom?
An atom has a net zero electrical charge, which indicates that it contains the same number of protons and electrons.
What causes an electron to move to a higher energy level?
An electron moves to a higher-energy orbital when it absorbs energy, such as heat or light.
What happens when an electron moves to a lower energy level?
When an electron moves to a lower-energy orbital, it emits energy.
What is measured in atomic absorption spectrophotometry? How does this differ from what is measured in emission spectroscopy?
Atomic absorption spectrophotometry measures the frequency of light absorbed by an atom when one of its electrons moves to a higher orbital. Emission spectroscopy measures the frequency of light emitted by an atom when one of its electrons moves to a lower orbital.
What is an isotope?
Isotopes are atoms of the same element that have different numbers of neutrons in their respective nuclei. Isotopes have different atomic mass numbers.
List two ways in which isotopes differ from one another.
In addition, some isotopes of an element may be very stable, while others may be quite unstable and decay rapidly.
What causes radioactivity?
Radioactivity is the emission of radiation that accompanies the spontaneous disintegration of unstable nuclei.
List and define the three types of radiation.
The three types of radiation are alpha rays, beta rays, and gamma rays. Alpha rays are a type of radiation composed of helium atoms minus their orbiting electrons. Beta rays are a form of radiation consisting of electrons. Gamma rays are a high-energy form of electromagnetic radiation.
How does a nuclear reactor generate radioactive elements?
In a nuclear reactor, a source of neutrons bombards the atoms of an element to create radioactive isotopes of that element. When the nucleus of an atom captures a bombarding neutron, a new isotope is formed and the nucleus is now said to be activated. Many activated nuclei immediately begin to decompose and emit radioactivity.
Describe the process of neutron activation analysis. How does the process allow a forensic scientist to identify an isotope?
In neutron activation analysis, a forensic scientist measures the gamma-ray radioactivity produced by a specimen that has been bombarded with neutrons. This allows the forensic scientist to identify the sample because the gamma rays of each element are associated with specific and unique energy values.
What are the main advantage and the main weakness of neutron activation analysis?
What important information about the identity of a sample cannot be determined by emission spectroscopy, atomic absorption, or neutron activation?
What type of materials can be identified using X-ray diffraction? Why is this not a significant limitation when analyzing inorganic compounds?
What is the main drawback to X-ray diffraction?
How does a magnifying glass enlarge objects viewed through it?
A magnifying glass makes things appear larger by refracting, or bending, light rays as they pass from the air into the glass and back into the air.
What is the difference between a real image and a virtual image?
A real image is an image formed when light rays converge on a surface. An observer can see a real image with the naked eye. A virtual image cannot be seen directly, but only by an observer looking through a lens.
Why does a compound microscope produce greater magnification than a magnifying glass?
A compound microscope produces greater magnification because it uses two lenses to enlarge the object being viewed instead of just one.
How does the eyepiece lens contribute to magnification?
The eyepiece lens magnifies the real, enlarged image created by the objective lens, producing a greatly enlarged virtual image of the object.
What is vertical illumination and under what conditions would a forensic scientist use it to examine a sample? Why is it superior to transmitted illumination under such conditions?
Vertical illumination is illumination of a specimen from above. A forensic scientist would use vertical illumination when studying opaque specimens. Transmitted illumination can be used only with specimens that are transparent.
How does one calculate the magnification power of a compound microscope?
The total magnification power of a compound microscope is the product of the magnifying power of each lens.
What does numerical aperture (N.A.) measure?
Numerical aperture measures the ability of an objective lens to resolve details into separate images instead of one blurred image.
What is the difference between a lens with N.A. 1.0 and one with N.A. 0.5?
A lens with N.A. 1.0 can separate details at half the distance of a lens with N.A. 0.5.
Why might an examiner choose a microscope with a lesser magnification to study a specimen?
An examiner might first select a lower-magnification microscope to get a good general overall view of the specimen, then switch later to a higher-power microscope to study smaller portions of the specimen in more detail.
Briefly describe how a comparison microscope works and what it is used for.
The comparison microscope is two compound microscopes connected by a bridge that uses mirrors and lenses to combine the images from two objective lenses into a single image. It is used to make side-by-side comparison of specimens.
How did the comparison microscope make possible modern firearms examination?
The comparison microscope enabled firearms examiners to compare a side-by-side magnified view of two bullets and thus to determine whether they were fired by the same gun.
List two unique characteristics of the stereoscopic microscope.
The stereoscopic microscope presents a three-dimensional image of an object. Also, whereas the image formed by the compound microscope is inverted and reversed, the stereoscopic microscope forms a right-side-up image.
What is the most widely used microscope in the crime laboratory? What features make it particularly suited for examination of physical evidence?
The stereoscopic microscope is the most frequently used microscope in the crime laboratory. Its wide field of view and great depth of focus make it an ideal instrument for locating trace evidence. Its large working distance (the distance between the objective lens and the specimen) allows for the microscopic examination of big, bulky items
What happens to a light beam that passes through a polarizing crystal?
beam of light passing through a polarizing crystal emerges vibrating in only one plane.
What happens when plane-polarized light passes through a second polarizing crystal set perpendicular to the first crystal?
When plane-polarized light passes through a second polarizing crystal set perpendicular to the first crystal, the light is blocked by the second crystal.
What is the main advantage of the microspectrophotometer?
The microspectrophotometer allows the forensic scientist to view a particle under a microscope while at the same time obtaining its absorption spectrum.
Explain how the infrared microspectrophotometer determines the identity of a specimen.
The infrared microspectrophotometer identifies a specimen by obtaining its IR spectrum, which is unique for every chemical substance.
What type of physical evidence is the microspectrophotometer typically used to analyze?
The technique is used to analyze fibers and paints.
What is the basic difference between a scanning electron microscope and the other microscopes used in the crime laboratory?
A scanning electron microscope uses a stream of electrons to create an image of the specimen being studied; all other microscopes use light coming off the specimen to create an image
How can a scanning electron microscope be used to identify the elements present in a specimen?
When the electron beam of the scanning electron microscope strikes a specimen, it creates X-rays that can be sorted by an X-ray analyzer. Because each element emits X-rays of characteristic energy values, the analyzer can identify the elements present in the specimen based on the energy values of the X-rays emitted by the specimen.
How can a scanning electron microscope be used to determine whether a suspect
has recently fired a gun?
Possible gunshot particles remaining on a shooter’s hands are lifted off with a piece of adhesive tape; the tape is then examined under the scanning electron microscope. The X-rays produced by the particles are analyzed and displayed according to their energies. This allows the examiner to detect the presence of elements frequently found in bullet primers.
Name two physiological factors and two nondrug factors that influence drug dependence.
Physiological factors- headaches and depression caused by withdrawal.

non-drug factors: person's expectations of the drug, societal responses or pressures to using.
Under what class of drugs is cocaine listed according to U.S. federal drug laws? Explain why this classification is pharmacologically incorrect.
Cocaine is listed as part of the narcotic range of drugs due to its association with socially unacceptable drugs. The drug itself is actually part of the stimulant class because it has a strong stimulant effect on the nervous system.
What is the source of most narcotic drugs? From what plant is this substance derived?
The source of most narcotic drugs is opium, which has a morphine content of 4-21%. It is derived from Papaver Somniferium, commonly known as poppy.
What opium derivative is most widely used by addicts? How is it typically administered? Give two reasons why this route of administration is popular.
The most commonly used opium derivate is heroin and is typically administered through intravenous injection. This administration route is more common both because it has a faster effect on the user and because it’s highly soluble in water which makes intravenous administration simple.
What is the most widely used illicit drug in the United States? Under what class of drugs is it listed and what are its short-term physical and psychological effects at low to moderate doses?
Marijuana - Schedule I
What is the most widely abused drug in the United States? Under what class of drugs is it listed and what are its short-term physical and psychological effects at low to moderate doses?
How can excessive use of depressants cause death?
Name the two most commonly abused illegal stimulants and the smokable forms of each.
Why does smoking provide a more intense drug experience than inhaling,or “snorting,” stimulants?
Name two club drugs that are associated with drug-facilitated sexual assault, rape, and robbery. Why are these drugs relatively easy to administer to an unsuspecting victim?
GHB and Rohypnol are central nervous system depressants that are often connected with drug-facilitated sexual assault, rape, and robbery. Both drugs are odorless, colorless, and tasteless and so will remain undetected when slipped into a drink.
What is the most popular club drug? Name three negative health effects associated with chronic use of the drug.
The most popular club drug is Ecstasy. Health effects associated with chronic use include seizures, muscle breakdown, stroke, kidney failure, cardiovascular system failure, and damage to the areas of the brain responsible for thought and memory.
On what three criteria does the Controlled Substances Act classify dangerous substances?
The Controlled Substances Act classifies dangerous substances on the basis of their potential for abuse, their potential for physical and psychological dependence, and their medical value.
According to the Controlled Substances Act, what is the legal difference between a schedule I drug and a schedule II drug?
Schedule I drugs have no accepted medical value in the United States; schedule II drugs may have medical use with severe restrictions.
What is a controlled substance analog? Why are such substances considered schedule I drugs?
What is a precursor?
How is possession of a precursor treated under the Controlled Substances Act?
List and describe the two phases in a criminalist’s scheme of action for identifying a drug.
What two goals must laboratory testing accomplish to positively identify a drug?
How does a color test work?
In a color test, a chemical reagent turns a specific color when brought into contact with a particular drug.
What is the main limitation of a color test for identifying drugs?
The main limitation of color tests is that they are useful for screening purposes only and are never taken as conclusive identification of unknown drugs.
Describe how a microcrystalline test works.
In a microcrystalline test, a drop of a chemical reagent added to a small quantity of drug on a microscopic slide produces crystals that are highly characteristic of the drug.
Name two advantages of microcrystalline tests.
Two advantages of these tests are that they are rapid and they often do not require the isolation of a drug from its diluents.
How are ultraviolet spectrophotometry and infrared spectrophotometry used in drug analysis?
Ultraviolet spectrophotometry is a useful technique for establishing the probable identity of a drug. Infrared spectrophotometry is one of the few analytical techniques available to the chemist that can specifically identify a substance.
Name two botanical features used to identify marijuana under a microscope.
Two botanical features used to identify marijuana include short “bear claw” hairs on the upper side of the leaf and longer, non-glandular hairs on the other side.
What method of examination is often used for marijuana when a microscopic examination cannot be obtained?
If microscopic examination cannot be obtained, thin-layer chromatography is often used to identify marijuana.
What is the primary duty of a forensic toxicologist?
Forensic toxicologists detect and identify the presence of drugs and poisons in body fluids, tissues, and organs.
What are the requirements of a suitable test for alcohol intoxication?
Tests for alcohol intoxication must be rapid and specific; they must be designed to test hundreds of thousands of motorists annually without causing them undue physical harm or unreasonable inconvenience; and they must provide a reliable diagnosis that can be supported and defended within the framework of the legal system
List at least three factors that determine the rate at which alcohol is absorbed into the bloodstream.
Factors that determine the rate at which alcohol is absorbed into the bloodstream include the total time taken to consume the drink, the alcohol content of the beverage, the amount of beverage consumed, and the quantity and type of food in the stomach at the time of drinking.
Name and describe the process by which most alcohol is eliminated from the body. How is the remaining alcohol eliminated and how is this useful in testing for alcohol?
Nearly all of the alcohol consumed is eventually oxidized to carbon dioxide and water. The remaining alcohol is excreted unchanged in the breath, urine, and perspiration. The fact that the amount of alcohol exhaled in the breath is in direct proportion to the concentration of alcohol in the blood has led to the development of instruments that quickly, easily, and reliably measure breath for its alcohol content.
Why is a blood test for alcohol taken shortly after drinking more advantageous for the suspect than one taken 30 minutes or more after drinking?
The administration of a blood test for alcohol requires drawing blood from a vein, but alcohol in the veins diffuses very rapidly into body tissues during the early phases of absorption compared to blood in the arteries. Thus, blood from a vein can show a misleadingly low alcohol concentration immediately after drinking.
What was the first successful breath-test device and what did it measure to determine blood-alcohol concentration? What is the main difference between this device and the breath-test devices currently in use?
The first successful breath-test device was the Breathalyzer. It measured the concentration of alcohol in alveolar breath. The Breathalyzer used chemical reactions to detect the presence of alcohol, whereas most modern testing devices use infrared radiation.
Describe how a fuel cell detector measures blood alcohol.
In a fuel cell detector, alcohol in a suspect’s breath combines with oxygen in the air to produce acetic acid. This process generates an electrical current that is proportional to the quantity of alcohol present in the breath.
What is the key to the accuracy of a breath tester? Describe two steps the operator
takes to ensure that this key requirement is met.
The key to the accuracy of a breath test is to ensure that the device captures the alcohol in the alveolar breath (deep-lung breath) of the subject. This is typically accomplished by programming the unit to accept a minimum amount of breath (no less than 1.5 liters) from the subject. Also, the subject must blow for a minimum time with a minimum breath flow rate.
What is a divided-attention task? Name and describe two divided-attention tasks often administered during field sobriety tests.
A divided-attention task tests a subject’s ability to comprehend and execute two or more simple instructions at one time. The walk and turn test requires the suspect to walk a straight line, touching heel to toe for nine steps, then turn around on the line and repeat the process. The one-leg stand requires the suspect to stand on one foot while holding the other foot several inches off the ground for 30 seconds and simultaneously counting out loud
What is horizontal gaze nystagmus and how does the test for it reveal blood-alcohol levels?
Horizontal gaze nystagmus is an involuntary jerking of the eye as it moves to the side. The subject is asked to follow an object with his or her eye as far to the side as the eye can go. The higher a person’s blood-alcohol concentration, the less the eye has to move toward the side before jerking or nystagmus begins.
What substances are typically added to blood that is collected from a subject before it is sent to a toxicology lab, and why are they added?
An anticoagulant usually is added to blood collected from a subject to prevent it from clotting. A preservative is also added to inhibit the growth of microorganisms capable of destroying alcohol in the blood.
Why is it best to collect blood samples from different body sites for post-mortem alcohol determination?
It is best to collect a number of blood samples from different body sites because ethyl alcohol may be generated in a deceased individual as a result of bacterial action.
At what blood-alcohol level is a typical driver in the United States considered legally intoxicated?
A typical driver in the United States is considered legally intoxicated at a blood alcohol level of 0.08 percent.
At what blood-alcohol level is a commercial truck or bus driver in the United States considered legally intoxicated?
A commercial truck or bus driver in the United States is considered legally intoxicated at a blood-alcohol level of 0.04 percent.
List two significant challenges a forensic toxicologist faces when attempting to identify drugs present in a body.
The forensic toxicologist often has no clue as to which drug or drugs may be present. Also, by the time a drug specimen reaches the toxicology laboratory, it has been dissipated and distributed throughout the body, so the toxicologist must work with very small amounts of drugs.
What is metabolism and how does it complicate the task of the forensic toxicologist?
Metabolism is the process by which the body changes one chemical to another in order to facilitate its elimination from the body. Because of metabolism, few substances enter and completely leave the body in the same chemical state.
Why is it necessary to follow a positive screening test for drugs with a confirmation test? What is the confirmation test of choice?
A follow-up test is required after a positive screening test to ensure that the positive result was not caused by a substance with a chemical structure similar to that of an illegal drug. Gas chromatography/mass spectrometry is generally accepted as the confirmation test of choice.
What is the A-B-O system? Why is the system no longer used by forensic scientists?
The A-B-O system is a system for classifying blood according to general groups or types. Forensic scientists no longer use it because DNA identification has replaced the A-B-O system as the most accurate means of linking blood evidence to an individual.
What is an antigen and how is it useful in individualizing blood?
An antigen is a substance, usually a protein, that stimulates the body to produce antibodies against it. The surface of every blood cell contains antigens that can be grouped into systems depending on their relationship to one another. The combination of antigens on blood cells serves as a basis for comparing blood samples.
What is an antibody and what happens when an antibody reacts with its specific antigen?
An antibody is a protein that destroys or inactivates a specific antigen. When an antibody reacts with its specific antigen the two immediately combine, causing the antibody to attach itself to the blood cell containing the antigen.
What factor is most whole blood typed for?
Most whole blood is typed for its A-B-O identity.
What is the most common blood type in the United States? Which is least common?
Type O blood is the most common in the United States; type AB is the least common.
For what other application do forensic scientists often use specific antigen–antibody reactions?
Specific antigen–antibody reactions are used to detect drugs in blood and urine.
What is the EMIT technique frequently used for, and what is its greatest limitation?
One of the most frequent uses of the EMIT technique in forensic laboratories has been for screening the urine of suspected marijuana smokers. The greatest problem associated with the technique is determining when the individual actually used marijuana.
What is the difference between monoclonal and polyclonal antibodies? Which type are more useful for the forensic scientist and why?
Monoclonal antibodies bind to only one specific antigen site; polyclonal antibodies can bind to a number of different sites on an antigen. Monoclonal antibodies are more useful because they can be used to create antigens for specific substances that the forensic scientist may need to test for, such as illegal drugs.
What three questions must the criminalist be prepared to answer when examining dried blood?
1. Is it blood?
2. From what species did the blood originate?
3. If the blood is of human origin, how closely can it be associated with a particular individual?
List two commonly used color tests for blood. How does a luminol test differ from these tests?
Two commonly used color tests for blood are the Kastle-Meyer test and the Hemastix test. Luminol testing differs from these techniques because the reaction of luminol with blood results in the production of light rather than color.
What is the purpose of a precipitin test?
A precipitin test is used to determine whether a bloodstain is of human or animal origin.
Name three strengths of precipitin tests.
1. It is very sensitive
2. It requires only a small amount of blood for testing
3. Human bloodstains dried for years may still give a positive reaction.
What is a genotype?
A genotype is the particular combination of genes present in the cells of an individual.
How do parents’ genotypes affect the blood type of their offspring? In what area of the law does this information have important implications?
Because each parent passes its genes to its offspring, and blood type is determined by genes, a child cannot have a gene for a blood type that does not appear in either of its parents. This fact has important implications in resolving cases of disputed paternity.
What is acid phosphatase and how is it used by forensic scientists?
Acid phosphatase is an enzyme that is secreted by the prostate gland into seminal fluid. It is used by forensic scientists to determine the presence of semen in a stain.
List three reasons why spermatozoa are often not found in seminal fluid collected at a crime scene.
1. Spermatozoa bind tightly to cloth materials such as underwear
2. Spermatozoa are extremely brittle when dry and easily disintegrate if the stain is washed or rubbed;
3. Sexual crimes may involve males who have an abnormally low—or even zero—sperm count.
Why is it important for investigators to seek information about when and if voluntary sexual activity last occurred before a sexual assault?
What is complementary base pairing?
Complementary base pairing is the specific pairing of adenine with thymine and cytosine with guanine in DNA.
What is the importance of the order in which base pairs are arranged?
The order in which base pairs are arranged defines the role and function of a DNA molecule.
How are proteins formed?
Proteins are formed by linking a combination of amino acids.
What determines the shape and function of a protein?
The sequence of amino acids in a protein chain determines the shape and function of the protein.
List three advantages gained from decoding the human genome.
Decoding the human genome can be useful for diagnosing and treating genetic diseases; it is crucial for understanding the underlying causes of cancer; and comparing the human genome with that of other organisms will help us understand the role and implications of evolution.
Describe the process of DNA replication.
DNA replication begins with the unwinding of the DNA strands in the double helix. Each strand is then exposed to a collection of free nucleotides. The double helix is re-created as the nucleotides are assembled in the proper order (A with T and G with C).
What is the importance of DNA replication?
The result is the emergence of two identical copies of DNA. DNA replication allows a cell to pass on its genetic identity when it divides.
What is polymerase chain reaction (PCR) and how is it useful to forensic scientists?
PCR is a technique for replicating or copying a portion of a DNA strand outside a living cell. The ability to multiply small bits of DNA with PCR means that sample size is no longer a limitation for the forensic scientist attempting to characterize DNA recovered from crime-scene evidence.
What are tandem repeats and how are they useful to the forensic scientist?
Tandem repeats are regions of a chromosome that contain multiple copies of a core DNA sequence arranged in a repeating fashion. Tandem repeats are useful for the forensic scientist because they provide a way to distinguish one individual from another through DNA typing.
What are short tandem repeats (STRs) and what are their significance to DNA typing?
STRs are locations (loci) on the chromosome that contain a short sequence core that repeats itself within the DNA molecule and that serve as helpful markers for identification.
List two advantages STRs have over restriction fragment length polymorphisms (RFLP).
1. The shorter DNA strands found in STRs are likely to be more stable and less subject to degradation
2. STRs can be amplified by PCR
What is multiplexing and why is it used in DNA profiling?
Multiplexing is a technique that simultaneously detects more than one STR in a single DNA analysis. Multiplexing is important to DNA profiling because the more STRs a forensic scientist can characterize, the greater the likelihood that they originated from the same individual.
What characteristics are revealed by the amelogenin gene and Y-STRs?
The amelogenin gene can reveal the sex of the person who contributed a DNA sample. Y-STRs are male specific and are useful for characterizing multiple-male DNA mixtures.
What are the three main differences between nuclear DNA and mitochondrial DNA?
Nuclear DNA is found only in the nucleus of the cell, is arranged in a continuous strand of bases, and is contributed by both parents. Mitochondrial DNA (mtDNA) is found outside the nucleus of the cell, is arranged in a circular loop of bases, and is contributed only by the mother.
Name two advantages of mitochondrial DNA analysis compared to nuclear DNA analysis.
1. Mitochondrial DNA is much more abundant in the body than is nuclear DNA
2. mtDNA analysis is significantly more sensitive than nuclear DNA profiling
Name two disadvantages of mitochondrial DNA analysis compared to nuclear DNA analysis.
1. Individuals of the same maternal lineage are indistinguishable by mtDNA analysis
2. mtDNA typing does not approach STR analysis in its discrimination power
How should packages containing DNA evidence be stored? Name one common exception and explain why it should be handled differently and how it should be stored.
All packages containing DNA evidence should be refrigerated or stored in a cool location out of direct sunlight until delivery to the laboratory. One common exception is blood mixed with soil. Microbes present in soil rapidly degrade DNA, so blood in soil must be stored in a clean glass or plastic container and immediately frozen
List four steps an investigator should take to prevent contamination of DNA evidence.
1. Change gloves before handling each new piece of evidence
2. Collect a substrate control for possible subsequent laboratory examination
3. Pick up small items of evidence such as cigarette butts and stamps with clean forceps
4. Package each item of evidence in its own well-ventilated container.
How is the hair cuticle used to identify different animal species?
The cuticle is formed by overlapping scales that occur in a variety of patterns in different animal species.
What aspect of the hair cortex is most important for the criminalist and why?
The cortex derives its major forensic importance from the fact that it is embedded with the pigment granules that impart hair with color. The color, shape, and distribution of these granules provide the criminalist with important points of comparison among the hairs of different individuals.
What is the follicular tag and why is it important to forensic scientists studying hair?
The follicular tag is a translucent piece of tissue surrounding the hair’s shaft near the root. It contains the richest source of DNA associated with a hair.
In comparing two hair samples, what aspects of the hair is the criminalist particularly interested in matching? What other features of hair are important to compare?
In comparing hair, the criminalist is particularly interested in matching the color, length, and diameter. Other important features to compare are the presence or absence of a medulla and the distribution, shape, and color intensity of the pigment granules in the cortex.
Which of the following cannot be confidently determined by a microscopic examination of hair: age, sex, racial origin, the part of the body from which the hair came, or whether the hair was pulled out or fell out?
Sex and Age
Why are most hair specimens collected at crime scenes not good sources of DNA?
Most in hair specimens are in the telogen stage because they contain the least amount of DNA
What type of hair specimens are potentially the richest source of nuclear DNA and why?
What is mitochondrial DNA and why is it useful in analyzing hair samples?
List three important considerations when submitting hair samples to a crime laboratory.
How has mass production limited the value of fiber evidence?
Many goods are made from almost identical fibers, making it difficult to provide individual identification of specific fibers with any degree of certainty.
What is the first and most important step in the examination of fiber?
The first and most important step in the examination is a microscopic comparison for color and diameter using a comparison microscope.
What physical characteristics of fiber might help an examiner identify it?
Other features that could aid in comparison are lengthwise striations on the surface of some fibers and the pitting of the fiber’s surface with particles added in the manufacturing process to reduce shine. The cross-sectional shape of a fiber may also help characterize the fiber.
How can microspectrophotometry and chromatography be used to analyze fiber evidence?
Microspectrophotometry can be used to compare the colors of fibers through their spectral patterns. Using chromatography, the forensic scientist can separate the constituents of dyes found in two fabric samples and compare them for similarity
Name two analytical devices used by forensic scientists to determine the class of a fiber.
The polarizing microscope and the infrared microspectrophotometer are both used to determine the class of a fiber.
How does the way most automobile manufacturers paint their cars help in the forensic comparison of automobile paint?
Manufacturers apply a variety of coatings to the body of an automobile, which adds significant diversity to automobile paint.
What three features of paint does a forensic scientist compare using a microscope?
1. Color
2. Surface texture
3. Color layer sequence.
Why is layer structure important for evaluating the significance of paint evidence?
When paint specimens possess colored layers that match in number and sequence of colors, the examiner can begin to think confidently in terms of relating the paints to a common origin.
What is the greatest shortcoming in using layer structure to analyze paint evidence?
The shortcoming of analysis of paint layer structures is that most paint specimens presented to the criminalist do not have a layer structure sufficiently complex to allow individualization to a single source.
How is pyrolysis gas chromatography used to distinguish one paint binder formulation from another?
In pyrolysis gas chromatography, heat is used to break apart the chain of polymers that make up the paint binder. The decomposed products of the polymer are swept through a gas chromatograph, which records a pattern of the separated products of the polymer.
What is PDQ and how is it used in identifying paint samples?
PDQ (Paint Data Query) is a computerized database maintained by the Royal Canadian Mounted Police Forensic Laboratories that contains information about automotive paint layer colors, primer colors, and binder composition. PDQ allows an analyst to obtain information on paints related to automobile make, model, and year.
Where is most paint evidence likely to be found?
Paint evidence is most likely to be found on or near people or objects involved in hit-and-run incidents.
Why is it important that paint evidence from a hit-and-run accident be collected close to the area of the car that was suspected of being in contact with the victim?
Because other portions of the car may have faded or been repainted.
List three factors that make investigating arson and explosions particularly difficult for forensic scientists.
1. Arson and explosion incidents are committed at the convenience of a perpetrator who has thoroughly planned the act
2. The perpetrator has left the scene long before an investigation is launched
3. The extensive destruction that frequently dominates the crime scene makes it more difficult to obtain proof of the commission of the offense.
What happens to the atoms of a molecule that undergoes a chemical reaction?
In a chemical reaction, the atoms of a molecule are rearranged to form new substances, or products.
How is energy consumed in a chemical reaction?
Energy is consumed in a chemical reaction when the bonds holding the atoms of the original molecules together are broken.
How is energy released in a chemical reaction?
Energy is released when the bonds between atoms re-form to create new products as a result of the reaction.
What is the energy barrier and how does it relate to the concept of ignition temperature?
The energy barrier is the minimum amount of energy required to initiate a chemical reaction. Ignition temperature is the minimum temperature at which a fuel spontaneously ignites. Thus, the energy barrier for any fuel is directly related to its ignition temperature.
How does the speed of an oxidation reaction affect its ability to produce a flame?
The faster an oxidation reaction takes place, the greater the likelihood it will produce a flame.
What factors influence the speed of the reaction?
Factors that influence the speed of the reaction include the physical state of the fuel and the temperature.
What physical state must a fuel occupy in order to produce a flame? Why can it produce a flame only in this state?
Fuel must be in a gaseous state to produce a flame, because only in the gaseous state can its molecules collide frequently enough to support a flaming fire.
Define and describe the process of pyrolysis.
Pyrolysis is the decomposition of organic matter by heat. In pyrolysis, heat causes solid organic matter to decay. This generates gaseous products that can combine with oxygen to produce a fire. The heat from the fire pyrolyzes more solid fuel into volatile gases, which sustains the fire.
What are oxidizing agents and why are they used in explosives?
An oxidizing agent is a substance that supplies oxygen to a chemical reaction. An explosion occurs so rapidly that oxygen in the air cannot participate in the reaction. For this reason, many explosives must have their own source of oxygen in order to produce the chemical reaction necessary to create an explosion.
Why is it important that the arson investigator begin examining a fire scene for signs of arson as soon as the fire has been extinguished?
Most arsons are started with petroleum-based accelerants that may evaporate within a matter of days or even hours.
What is the primary focus of a fire-scene search and why?
A search of the fire scene must focus on finding the fire’s origin, because this area will prove most productive in any search for an accelerant or ignition device.
What evidence at a fire site may indicate the possibility of arson?
Some telltale signs of arson include evidence of separate and unconnected fires; use of “streamers”—such as a trail of gasoline or paper—to spread the fire from one area to another; the presence of containers capable of holding an accelerant; finding a potential ignition device; and the existence of an irregular-shaped pattern on a floor or on the ground caused by pouring an accelerant onto the surface.
Where will an investigator usually locate the probable point of origin of a fire?
The probable origin of a fire will most likely be located closest to the lowest point that shows the most intense characteristics of burning.
What factors can cause a fire to deviate from normal behavior?
Factors that can cause a fire to deviate from normal behavior include prevailing drafts and winds; secondary fires caused by collapsing floors and roofs; the physical arrangement of the burning structure; stairways and elevator shafts; holes in the floor, wall, or roof; and the effects of the firefighters in suppressing the fire
Why are some traces of the accelerants used in an arson usually found even after intense fires?
When an accelerant is poured over a large area, some of it is likely to seep into porous surfaces such as cracks in the floor, upholstery, rags, plaster, wallboards, and carpet, where enough of it remains unchanged that it can be detected in the crime laboratory.
Why might an investigator conduct laboratory tests on unburned control material collected from a fire scene?
Laboratory tests may be made on unburned control material to analyze the breakdown products caused by the material’s exposure to intense heat during the fire.
Describe the headspace technique for recovering accelerant residues.
In the headspace technique, an airtight container holding debris from the fire scene is heated, vaporizing any volatile residue present in the debris and trapping the vapor in the container’s enclosed airspace. The vapor, or headspace, is removed with a syringe.
What instrument is most often used to detect and characterize recovered flammable residues?
A gas chromatograph is usually used to detect and characterize residues in the vapor.
What produces the violent physical disruption of the surrounding environment released in an explosion? Explain how this creates shrapnel when a bomb explodes.
The sudden buildup of expanding gas pressure at the origin of an explosion produces the violent physical disruption of the surrounding environment. In a bomb, the extremely high pressure caused by the expanding gases pushes on the walls of the bomb, stretching and finally shattering them. The pieces of the walls are shattered and thrown outward in all directions by the force of the explosion, creating shrapnel.
What is an oxidizing agent?
An oxidizing agent is a chemical that supplies oxygen to a reaction.
Why is an oxidizing agent important to an explosion?
Oxidizing agents are important to explosions because detonation occurs so rapidly that oxygen in the air cannot participate in the reaction; thus, many explosives must have their own source of oxygen.
What characteristic of an explosive determines whether it is classified as a low explosive or a high explosive? How is this reflected in the type of pressure wave produced by the explosive?
The speed at which an explosive decomposes determines its classification as a low or high explosive. Low explosives produce a subsonic pressure wave, whereas high explosives produce a supersonic pressure wave.
Name two types of low explosives and list the ingredients of each.
Black powder - potassium nitrate, carbon, and sulfur
Smokeless powder - nitrocellulose and either nitroglycerin or nitrated cotton.
Why does black powder not explode unless it is ignited in a confined area? What practical application besides explosives does this make black powder suitable for?
Black powder does not explode when unconfined because it decomposes too slowly. This makes black powder suitable for use in safety fuses, in which it carries a flame to an explosive charge.
What are primary explosives and what are they used for?
A primary explosive is a high explosive that is easily detonated by heat or shock. They are used to detonate the most commonly used high explosives, which are known as secondary explosives.
What is a detonator?
What is the most common form of detonator?
What role does ammonium nitrate play in water gels, emulsions, and ANFO explosives?
In what commercial form can ammonium nitrate be readily obtained?
In what liquid does a forensic scientist rinse debris recovered from an explosion site and why?
A forensic scientist rinses debris from an explosion site in acetone because most explosives are highly soluble in acetone. This allows the scientist to quickly remove any traces of explosive from the debris so they can be isolated and identified.
What type of materials can be identified using X-ray diffraction?
X-ray diffraction can be applied only to the study of solid, crystalline materials— that is, solids whose atoms have a definite and orderly arrangement.
What are taggants and how are they used to identify explosives?
Taggants are tiny color-coded chips added to commercial explosives during the manufacturing process. Some of these chips would be expected to survive an explosion and be recovered at explosion scenes. The taggants in an explosive are arranged in a color sequence that indicates where the explosive was made and when it was produced
Who published the first book on the science of fingerprinting? What were the book’s most important contributions to understanding fingerprints?
Francis Galton published the first book on the subject of fingerprinting. The book’s most important contributions were to demonstrate that no two prints are identical and that an individual’s prints remain unchanged from year to year.
What major advance in fingerprint technology was pioneered by Juan Vucetich and Sir Richard Henry? What was the importance of this advance?
Vucetich and Henry pioneered the creation of classification systems capable of filing many thousands of prints in a logical and searchable sequence. This allowed law enforcement officials to quickly compare prints found at a crime scene to those of known criminals as an aid to identifying potential suspects.
What aspect of a fingerprint determines its individuality?
The identity, number, and relative location of ridge characteristics impart individuality to a fingerprint.
What is the dermal papillae and why is it important in fingerprinting?
Why is it almost impossible to obscure one’s fingerprints by surgery or mutilation?
Describe each of the three classes of fingerprints. Which class is the most common in the population? Which is least common?
What aspect of a fingerprint forms the basis for primary classification under the FBI system?
The presence or absence of the whorl pattern is the basis for determining the primary classification in the FBI system.
What is the main drawback of the FBI fingerprinting system?
The main drawback of the FBI system is that it is useful only when a full set of fingerprints is available.
Briefly describe how the Automated Fingerprint Identification System (AFIS) creates a fingerprint image.
AFIS scans fingerprints and converts them into digital images that contain data on the relative location and orientation of ridge characteristics.
What characteristics of the fingerprint does the AFIS record for comparison?
The system records the points where ridges terminate, the points where they branch into two ridges, and the relative position and orientation of each ridge characteristic.
What is the final step in fingerprint identification? Why is this step necessary if a computerized database of fingerprints is available to the forensic scientist?
The final step in fingerprint identification is always visual comparison of the prints in question by a trained examiner. A computer database can only produce a list of prints that are similar to the print in question; it cannot make a positive identification.
List and describe the three types of fingerprints that may be found at a crime scene.
Visible prints are made when a finger deposits a visible material such as ink, dirt, or blood onto a surface. Plastic prints are ridge impressions left on a soft material such as putty, wax, soap, or dust. Latent or invisible prints are impressions caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object.
List two types of specialized fingerprint powders and name one advantage each has over traditional fingerprint powder.
Two specialized fingerprint powders are magnetic-sensitive powder and fluorescent powder. Using magnetic-sensitive powder offers less chance that the print will be destroyed or damaged because the powder is spread using a magnetic brush that has no bristles to come in contact with the surface containing the print. Fluorescent powders reveal a vivid image of a print under ultraviolet light. When the developing print is photographed under UV light, the color of the surface will not obscure the print
What is the most commonly used chemical method to visualize latent fingerprints on porous materials? If this method is unsuccessful, what other technique typically
is used?
The ninhydrin method is most commonly used to visualize latent fingerprints on porous materials. If the ninhydrin method fails, the Physical Developer technique typically is used.
What phenomenon underlies many of the new chemical techniques used to visualize latent fingerprints? Why is this phenomenon so valuable in fingerprint visualization?
The phenomenon of fluorescence serves as the underlying principle of many of the new chemical techniques used to visualize latent fingerprints. Substances that emit light or fluoresce are more readily seen either with the naked eye or through photography as compared to non-light-emitting materials.
When should a fingerprint be “lifted” from a crime scene?
A print should be “lifted” from a crime scene when it is on a large, immovable object.
Describe how to lift and preserve a fingerprint using adhesive tape.
Dust the print with fingerprint powder, then cover the print with adhesive tape. When the tape is pulled up, the powder is transferred to the tape. Then the tape is placed on a card that provides a good background contrast with the powder.
What is digital imaging and how is it used in fingerprint analysis?
Digital imaging is a process through which a picture is converted into a series of square electronic dots known as pixels. It is used to compare fingerprints and to enhance poor fingerprint images.
What is the greatest limitation to digital imaging?
The main limitation of digital imaging is that it is only as useful as the images it has to work with.
List three class characteristics of a gun barrel.
Three class characteristics of a gun barrel are its caliber, the number of lands and grooves, and the direction and twist of the lands and grooves.
Describe how a firearms examiner compares two bullets.
The examiner places both bullets under a comparison microscope, pointing in the same direction, and then rotates one bullet until a well-defined land or groove comes into view. When the examiner locates striation markings on this bullet, the other bullet is rotated until a matching region is found. When a matching area is located, the two bullets are simultaneously rotated to locate additional matching areas around the periphery of the bullets.
What characteristic does an examiner most often use to identify bullets and why?
The examiner uses the striation markings to identify bullets because no two rifled barrels have identical striation markings.
List two reasons why striations on bullets fired from the same gun may vary slightly.
The presence of grit and rust can alter the markings on bullets fired through the same barrel. Striation markings on a barrel are not permanent structures; they are subject to continuing change and alteration through wear as succeeding bullets traverse the length of the barrel.
Besides the barrel, what parts of a firearm may leave distinctive markings on a shell cartridge?
The firing pin, the breechblock, the extractor, the ejector, the magazine, the clip, and the fire chamber walls may all leave distinctive markings on a shell casing.
Why does a firearms examiner test-fire bullets from a suspect barrel?
The examiner must test-fire bullets through the suspect barrel because there is no other practical way to directly compare the markings on the fired bullet and those found within a barrel.
What is distance determination?
The examiner must test-fire bullets through the suspect barrel because there is no other practical way to directly compare the markings on the fired bullet and those found within a barrel.
Describe two situations in which distance determination can establish the facts of a shooting incident.
If a suspect pleads self-defense as the motive for a shooting, determining how far apart the suspect and victim were at the time of shooting can establish the facts of the incident. Distance determination can also determine whether a shooting was suicide
What evidence does an investigator study to make a distance determination?
The distribution of gunpowder particles and other discharge residues around the bullet hole permits an assessment of the distance from which a handgun or rifle was fired.
How can test-firing a suspect weapon help the investigator make a distance determination?
By comparing residue patterns from test firings to those found at the crime scene, the examiner may find enough similarity in shape and density on which to base an opinion as to the distance from which the shot was fired.
List three characteristics of a bullet hole that indicate that the shot was fired at extremely close range.
1. A heavy concentration of smokelike vaporous lead usually surrounds the bullet entrance hole
2. Loose fibers surrounding a contact hole show scorch marks from the flame discharge of the weapon, and some synthetic fibers show signs of being melted as a result of the heat from the discharge. 3. The blowback of muzzle gases may produce a stellate (star-shape) tear pattern around the hole.
What is the Greiss test and what two pieces of information can it provide to an investigator?
How is shot pattern used to make a distance determination for shotgun blasts?
What factors other than distance to target can affect the distance determination?
What evidence do investigators look for when trying to determine whether a suspect has fired a handgun?Where is such evidence typically found and why?
Why does analysis of primer residue from a suspect’s hands produce a low rate of positive results?
Why is such analysis typically ineffective in locating primer residue from a .22-caliber gun?
Describe how a criminalist restores an obliterated serial number on a weapon.
To restore an obliterated serial number, the criminalist applies a suitable etching agent to the area that has been defaced. The metal in this area dissolves at a faster rate than the unaltered metal surrounding it, thus permitting the etched pattern to appear in the form of the original numbers.
Why would an investigator not pick up a weapon by its barrel with a pencil or stick in order to protect latent fingerprints? How should suspect firearms be handled in such a situation?
An investigator would not pick up a weapon by its barrel with a pencil or stick in order to protect fingerprints because this may disturb powder deposits, rust, or dirt lodged in the barrel, and consequently may alter the striation markings on test-fired bullets. If the recovery of latent fingerprints is a primary concern, it is best to hold the weapon by the edge of the trigger guard or by the checkered portion of the grip.
What characteristics of a suspect firearm should an investigator record before unloading it?
The investigator should record the weapon’s hammer and safety position as well as the location of all fired and unfired ammunition in the weapon.
Why should the investigator number the chambers and cartridges when unloading a suspect weapon?
The cylinders and cartridges should be numbered because this information may be useful to determine the sequence of events, particularly in cases in which several shots were fired.
What is the investigator’s primary concern when collecting and handling bullets and cartridge cases?
The protection of class and individual markings on bullets and cartridge cases must be the primary concern of the field investigator who is handling such evidence.
Why must the investigator exercise extreme caution when removing a bullet lodged in a wall or other object?
If the bullet’s surface is accidentally scratched when removing it from a wall or other object, valuable striation markings could be obliterated that can help link the bullet to a suspect weapon.
Name two types of marks that impart individuality to a tool and explain how the marks are made.
What techniques does an investigator use to analyze tool marks that cannot be removed from a crime scene? What is the disadvantage of this technique?
What is the first thing the investigator does before handling or moving any impression at a crime scene? Why is this considered merely a backup or precautionary procedure?
What kinds of impression evidence might a forensic odontologist be asked to analyze? How might this help identify a suspect?