Exam 3

Question 1

Aztec gold case

Answer 1

hit & run with unidentified vehicle, gold metallic painted plastic fragments, fournier transform infrared spectroscopy, consistent with 1997 Ford Mustang through PDQ, and improvement in vehicle manufacturer safety standards (e.g. automatic braking)

Question 2

Night Stalker case

Answer 2

murders, sexual assaults, kidnappings, casts of shoe prints were found at some scenes, his stolen car was tracked down and usable fingerprints were found through superglue fumigation, and ballistic evidence matched multiple crime scenes

Question 3

How does a magnifying glass enlarge objects viewed through it?

Answer 3

light bends as they pass through the lenses and converge

Question 4

What is the difference between real image and virtual images?

Answer 4

real image = image viewed directly, virtual image = magnified image through the lens

Question 5

Why does a compound microscope produce greater magnification than a magnifying glass? How does the eyepiece lens contribute to magnification?

Answer 5

two lenses = greater magnification

Question 6

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?

Answer 6

illumination from above, used when studying opaque specimens, transmitted illumination can only be used with transparent specimens

Question 7

How does one calculate the magnification power of a compound
microscope?

Answer 7

multiple objective X ocular

Question 8

What does numerical aperture (N.A.) measure? What is the difference between a lens with N.A. 1.0 and one with N.A. 0.5?

Answer 8

measures the ability of an objective lens to resolve details into separate images instead of one blurred image, 1.0 can separate details at half the distance of 0.5

Question 9

Why might an examiner choose a microscope with a lesser
magnification to study a specimen?

Answer 9

if the object doesn’t require high magnification or needs comparison

Question 10

How do comparison microscopes work and when is it used?

Answer 10

2 independent objective lenses joined together by a bridge to a common ocular lens, usually for firearm examination or bigger objects

Question 11

How did the comparison microscope make modern firearms examination possible?

Answer 11

side-by-side magnified view of bullets

Question 12

List two unique characteristics of the stereoscopic microscope.

Answer 12

look through both ocular lenses simultaneously and large working distance

Question 13

What is the most widely used microscope in the crime laboratory? What features make it particularly suited for examination of physical evidence?

Answer 13

stereoscopic microscope and it’s good for big items

Question 14

What is the main advantage of the micro-spectrophotometer?

Answer 14

can obtain both visible and infrared spectrum of the specimen

Question 15

Explain how the infrared micro-spectrophotometer determines the identity of a specimen. What type of physical evidence is the
micro-spectrophotometer typically used to analyze?

Answer 15

obtaining infrared spectrum which is unique for every specimen then comparing in database & paint, fiber, and ink

Question 16

What is the basic difference between a scanning electron microscope and the other microscopes used in the crime laboratory?

Answer 16

bombards specimen with beam of electrons instead of light

Question 17

How can a scanning electron microscope be used to identify the elements present in a specimen?

Answer 17

each element will emit different x-ray emissions

Question 18

How can a scanning electron microscope be used to determine whether a suspect has recently fired a gun?

Answer 18

can measure the amount of barium & antimony

Question 19

List three class characteristics of a gun barrel.

Answer 19

lands & grooves, approx width, and twist direction

Question 20

Describe how a firearms examiner compares two bullets. What
characteristic does an examiner most often use to identify bullets and why?

Answer 20

uses comparison microscope, goal is to decide if a bullet was fired from a particular weapon, they use nicks, breaks, and wear

Question 21

List two reasons why striations on bullets fired from the same gun may vary slightly.

Answer 21

number of lands & grooves and twist direction

Question 22

Besides the barrel, what parts of a firearm may leave distinctive markings on a shell cartridge?

Answer 22

firing pin, breech-face, and ejector & extractor mechanism

Question 23

Why does a firearms examiner test-fire bullets from a suspect barrel?

Answer 23

best way to compare

Question 24

What is distance determination? Describe two situations in which
distance determination can establish the facts of a shooting incident.

Answer 24

distribution of gunpowder & residue will vary given how far away the gun was fired, e.g. suspect claims it was self-defense and they were fighting the victim, but bullet was fired from 3+ feet and suspect claims accidental but bullet was fired from less than a foot

Question 25

What evidence does an investigator study to make a distance determination?

Answer 25

gunpowder, residue, tear pattern, dark ring, and vaporous lead

Question 26

List three characteristics of a bullet hole that indicate that the shot was fired at extremely close range.

Answer 26

star-shaped tear pattern, vaporous lead, and specks

Question 27

What is the Greiss test and what two pieces of information can it provide to an investigator?

Answer 27

can detect gunpowder even if it's invisible, if gunpowder's present and distance from target

Question 28

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?

Answer 28

measuring the spread of the discharged shot and barrel length, pellets fired, powder charge used

Question 29

What evidence do investigators look for when trying to determine whether a suspect has fired a handgun? Where is such evidence found and why?

Answer 29

primer residue on the thumb web and back of firing hand

Question 30

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?

Answer 30

primer residue only remains for a short time & can be washed off and .22 caliber primer usually doesn't contain the same elements

Question 31

Describe how a criminalist restores an obliterated serial number on a weapon.

Answer 31

etching agent

Question 32

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?

Answer 32

it may disturb powder, rust, dirt, & may alter striations and by edge of trigger guard

Question 33

What characteristics of a suspect firearm should an investigator record before unloading it? Why should the investigator number the chambers and cartridges when unloading a suspect weapon?

Answer 33

hammer & safety positions, location of all fired & unfired ammunition and to determine sequence of events

Question 34

What is the investigator’s primary concern when collecting and handling bullets and cartridge cases? Why must the investigator exercise extreme caution when removing a bullet lodged in a wall or other object?

Answer 34

protection of class & individual markings and not to accidentally scratch

Question 35

Name two types of marks that impart individuality to a tool and explain how the marks are made.

Answer 35

ridges & valleys during manufacturing and nicks during normal use

Question 36

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?

Answer 36

photographed, marked to scale, & made a cast and clarity is lost

Question 37

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?

Answer 37

photographed in case anything is damaged

Question 38

What kinds of impression evidence might a forensic odontologist be asked to analyze? How might this help identify a suspect?

Answer 38

bite marks and if a sufficient number of similarities exist

Question 39

Define the terms physical property and chemical property.

Answer 39

a substance without reference to any other substance and behavior of a substance when it reacts or combines with another substance

Question 40

Why is the metric system of measurement easier to use than the “English system”? Which system is used in the United States?

Answer 40

everything is in increments of 10 and imperial system

Question 41

List the basic units of length, mass, and volume in the metric system.

Answer 41

centimeter, meter, & kilometer, miligram, gram, & kilogram, and milliliter & liter

Question 42

What reference points are most often chosen when constructing a temperature scale?

Answer 42

celsius boiling & freezing points of water

Question 43

List the two most commonly used temperature scales and their respective reference points.

Answer 43

celsius & fahrenheit and 0 & 100 degrees and 32 & 212 degrees

Question 44

Define weight and mass and explain the difference between the two concepts.

Answer 44

weight = force with which gravity attracts something & mass = amount of matter independent of gravity and mass is determined by comparison to known mass of standard objects

Question 45

Define element and compound; name the smallest unit of each.

Answer 45

element = simplest substance known & compound = 2+ atoms of different elements that join and atom & molecule

Question 46

What physical change occurs when a substance undergoes the following changes of state: (a) from liquid to solid, and (b) from liquid to gas?

Answer 46

freezing and evaporation

Question 47

Define sublimation. What happens to the attractive forces between molecules of a substance that undergo sublimation?

Answer 47

when a solid transforms directly into a gas and they decrease

Question 48

What is a phase and how can two different phases be distinguished from one another?

Answer 48

different states of matter and having no distinct boundaries

Question 49

What is density? How does heat affect the density of gases and liquids?

Answer 49

how much mass is in a given volume and it decreases it

Question 50

Define the terms refraction and refractive index.

Answer 50

bending of light waves because of velocity change and ratio of the velocity of light in a vacuum compared to the medium under examination

Question 51

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?

Answer 51

the atoms in a crystalline solid have regular arrangement while an amorphous doesn't and amorphous only has 1 refractive index while crystalline have 2

Question 52

Explain how a prism disperses white light into its constituent colors.

Answer 52

it reflects all colors

Question 53

Define intensive property & name two for matter.

Answer 53

a characteristic that doesn't depend on amount and density & boiling point

Question 54

What is color?

Answer 54

what light is reflected versus absorbed

Question 55

What two models do scientists use to explain the nature of light?

Answer 55

a continuous wave & a stream of discrete photons

Question 56

List two factors that make it difficult to compare glass samples.

Answer 56

most fragments are too small and most manufactured glass is fairly similar

Question 57

Describe the process of flotation and explain what it is used for.

Answer 57

a process used to compare glass's density and it's used to compare potential matches

Question 58

What is the Becke line and how is it used to determine the refractive index of a glass sample?

Answer 58

a bright halo around an object submerged in a liquid with a different refractive index of its own and by showing and disappearing it

Question 59

What is the 3R rule and how is it applied to the analysis of glass fractures?

Answer 59

radial cracks from a right angle on the reverse side of the force applied and it shows which side of glass was broken

Question 60

How can an investigator determine the order in which several successive penetrations of a glass occurred?

Answer 60

where the fractures end when they touch

Question 61

What is a trace element and why are trace elements important in analyzing physical evidence?

Answer 61

trace elements are when something is present in less than 1% concentration and they're invisible markers

Question 62

Explain how the analysis of trace elements was important to the investigation of the assassination of President John F. Kennedy

Answer 62

it linked the bullets that hit him and the governor to the same source

Question 63

Describe the difference between a continuous spectrum and a line spectrum. Which is most helpful in identifying a particular element and why?

Answer 63

a continous spectrum shows a blended picture while a line spectrum shows colors separated and a line spectrum is more helpful because it gives a unique & readable fingerprint

Question 64

Why do forensic scientists often use inductively coupled plasma (ICP) emission spectrophotometry to analyze mutilated bullets?

Answer 64

they're not suitable for traditional comparison microscopes

Question 65

List the three basic subatomic particles and indicate whether each has positive, negative, or no electrical charge.

Answer 65

protons +, electrons -, and neutrons /

Question 66

What is the net electrical charge of an atom? What does this indicate about the arrangement of subatomic particles in an atom?

Answer 66

0 and it means equal number of protons & electrons

Question 67

What causes an electron to move to a higher energy level? What happens when an electron moves to a lower energy level?

Answer 67

when it absorbs energy and when it emits energy

Question 68

What is measured in emission spectroscopy?

Answer 68

the frequency of light emitted when electrons lower

Question 69

What is an isotope? List two ways in which isotopes differ from one another.

Answer 69

atoms of the same elements that don't have the same amount of neutrons and mass & stability

Question 70

What causes radioactivity? List and define the three types of radiation

Answer 70

the emission of high energy subatomic particles with spontaneous disintegration of unstable isotope's nuclei and alpha, beta, & gamma

Question 71

How does a nuclear reactor generate radioactive elements?

Answer 71

a neutron colliding with an uranium atom causing it to split and release energy

Question 72

Describe the process of neutron activation analysis. How does the process allow a forensic scientist to identify an isotope?

Answer 72

measures gamma rays and because each element will have a unique measurement

Question 73

What is the main advantage and the main weakness of neutron activation analysis?

Answer 73

gives a way to identify trace elements and it is expensive and rare

Question 74

How does the way most automobile manufacturers paint their cars help in the forensic comparison of automobile paint?

Answer 74

many coatings provide uniqueness

Question 75

What three features of paint does a forensic scientist compare using a microscope?

Answer 75

color, surface texture, & layer sequence

Question 76

Why is layer structure important for evaluating the significance of paint evidence? What is the greatest shortcoming in using layer structure to analyze paint evidence?

Answer 76

when many layers match a match is more likely and most specimens don't have many layers

Question 77

How is pyrolysis gas chromatography used to distinguish one paint binder formulation from another?

Answer 77

polymer chains are broken up by heat and their chromatography is recorded

Question 78

What is PDQ and how is it used in identifying paint samples?

Answer 78

a database and can be compared and matched

Question 79

Where is most paint evidence likely to be found?

Answer 79

on or near victims of automobile crimes

Question 80

Why should paint evidence from a hit-and-run accident be collected close to the area of the car suspected of being in contact with the victim?

Answer 80

other areas of the car may be different

Question 81

How can soil evidence be valuable even if the site of the crime has not been ascertained?

Answer 81

it may give investigators an idea of where to look

Question 82

What is a mineral and how can minerals be important in the comparison of soil samples?

Answer 82

naturally occurring crystalline solid and combinations of minerals in soil differ by area

Question 83

What is the most important consideration when collecting soil samples from a crime scene? At what locations should soil standard/reference samples be collected?

Answer 83

establishing variation of soil and at the site, within a 100 foot radius, & at all possible related locations

Question 84

Why is soil collected from suspect automobiles left in lump form?

Answer 84

preserves buildup and layers