Forensics Chapter 3: Physical Evidence

What is comparison analysis? what are two steps in comparison?

A comparison analysis subjects a suspect specimen and a standard/reference specimen to the same tests and examinations to determine whether they have a common origin. The first step in comparison is to choose specific combinations of properties from the suspect and the standard/reference specimen for comparison. The sec on step is for the forensic scents to render a conclusion about whether the specimens come from the same source.

What is a forensic database and how are such databases useful to criminalists?

A forensic database is a computerized archive of information relating to a specific type of physical evidence. Such as databases make it much easier for a forensic scientist to link a suspect to the commission of a crime through comparative analysis of evidence.

Why does a forensic scientist often opt not to use the most sensitive analytical techniques when comparing suspect substances?

A forensic scientist often opts not to use the most sensitive analytical techniques when comparing suspect substances because, carried to the extreme, no two things in this work are alike in every detail. Measurements that are extremel sensitive may show differences between two samples that suggest the samples came from difference sources even though they actually came from the same source.

International Forensic Automotive Paint Data Query (PDQ)

contains chemical and color information pertaining to original automotive paints

National Integrated Ballistics Information Network (NIBIN)

contains records of markings made by firearms on bullets and cartridge casings recovered from crime scenes

Define individual characteristics and give two example.

individual characteristics are properties of evidence that can be attributed to a common source with an extremely high degree of certainty. Examples include the ridge on bullets or tools, irregular and random wear patterns in tire or footwear impressions, handwriting characteristics, and the irregular edges of broken objects

Combined DNA Index System (CODIS)

stores DNA profiles

Give at least three examples of a specialized task a criminalist might perform in crime-scene reconstruction.

1. using a laser beam to plot the approximate bullet path 2. blood spatter analysis 3. determining the direction of impact of projectiles penetrating glass objects 4. locating gunshot residues deposited on the victim's clothing to estimate the distance of a shooter from a target 5. searching for primer residues deposited on the hands of a suspect shooter

List 5 examples of each of the following types of physical evidence: biological materials, impressions, and manufactured items

Biological materials include blood,saliva, semen, DNA, hair, organs, and physiological fluids. Impressions include tire markings, shoe prints, depressions in soft soils, all other forms of tracks, glove and other fabrics impressions, tool marks, and bite marks. Manufactured items include firearms, ammunition, fibers, paint, glass, petroleum products, plastic bags, rubber, polymers, and vehicle headlights.

In which of the following ways can physical evidence aid in the crime-scene reconstruction?

A. by supporting or contradicting statement given by witnesses and/or suspects C. by confirming the accuracy of a crime-scene reconstruction to a jury E. by generating leads that may help investigators solve the case.

Define class characteristics and give two examples.

Class characteristics are properties of evidence that can be associated only with a group and never with a single source. Examples include paint chips, random glass fragments, blood, and artificial fibers.

What is crime scene reconstruction?

Crime-scene reconstruction is the method used to support a likely sequence of events by observing and evaluating physical evidence, as eel as statements made by those involved with the incident.

State two reasons why it is important to consider the relevance of scientific evidence before allowing it to be introduced into a criminal case.

It is important to consider the relevance of scientific evidence before allowing it to be introduced into a criminal case because physical evidence is accorded great weight during jury deliberations. In addition, failure to take proper safeguards when determining the relevance of evidence may unfairly prejudice a case against the accused.

List three reasons why it is not possible to define a simple analytical scheme that can be applied to all types of evidence.

It is not possible to define a simple analytical scheme that can be applied to all types of evidence because (1) each type of evidence obviously requires different tests; (2) each test has a different degree of specificity; and (3) the partitioner has little or no control over the quality and quantity of specimens received.

What is the first and most important step in crime-scene reconstruction?

Securing and protecting the crime scene

Describe the difference between the forensic and offender indexes in the CODIS database,

The forensic index contains DNA profiles from unsolved crime-scene evidence. The offender index contains the profiles of convicted or arrested individuals.

What is the greatest weakness of class physical evidence? What is the main reason for this weakness?

The greatest weakness of class physical evidence is that it cannot relate physical evidence to a common origin with a high degree of certainty. Evidence possessing class characteristics can be associated only with a group and never with a single source.

Who ultimately determines the significance of physical evidence in a trial?

The jury

What is the greatest value of class physical evidence?

The value of class physical evidence lies in its ability to corroborate events with data in a manner that is as nearly as possible, free of human error and bias.

State the product rule and explain how it applies to the comparison of physical evidence.

The product rule states that multiplying together the frequencies of independently occurring facts allows one to determine an overall frequency of occurrence for that combination of factors. The product rule can be used to show the likelihood of two pieces of evidence containing the exact same set of characteristics.

Explain how the product rule is relevant to the murder conviction of Wayne Williams.

The product rule suggests that, as the number of different objects linking an individual to a crime increases, the probability of that person being involved increases dramatically. In the case of Wayne Williams, twenty-eight different types of fibers linked Williams to several murder victims, making it extremely likely that Williams was responsible for the killings.

What is the purpose of identification? What are the two main requirements for identification?

The purpose of identification is to determine the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit. Identification first requires the adoption of testing procedures that give characteristic results for specific standard materials. Identification also requires that the number and type of tests needed to identify a substance be sufficient to exclude all other substances.

Shoeprint Image Capture and Retrieval (SICAR)

a comprehensive shoe sole database that include more than 300 manufacturers of shoes with more than 8000 different sole patterns.

Automated Fingerprint Identification System (AFIS)

a national fingerprint and criminal history system maintained by the FBI