Criminalistics: Physical Evidence (Chapter 3) - Video Notes Flashcards

Question-and-answer flashcards covering key concepts from the notes on physical evidence in criminalistics.

What is physical evidence as defined in forensic science?

Objects that can establish that a crime has occurred, or can link a crime to a victim or to a perpetrator; almost anything can qualify as physical evidence if properly recognized and preserved.

Why is recognition and preservation of physical evidence crucial?

If evidence is not recognized or properly preserved, no laboratory analysis can salvage the case, regardless of instrumentation or expertise.

What is the purpose of recognizing physical evidence?

To collect and analyze it for use in identification or in comparison.

Who decides the weight of physical evidence in a case?

Ultimately, the weight is decided by a jury.

Name examples of physical evidence types (part 1).

Blood, semen, and saliva; documents; drugs; explosives.

Name examples of physical evidence types (part 2).

Fibers; fingerprints; firearms and ammunition; glass.

Name examples of physical evidence types (part 3).

Hair; impressions; organs and physiological fluids; paint.

Name examples of physical evidence types (part 4).

Petroleum products; plastic bags; plastic, rubber, and other polymers.

Name examples of physical evidence types (part 5).

Powder residues; serial numbers; soil and minerals; tool marks; vehicle lights; wood and other vegetative matter.

What is the purpose of examining physical evidence?

Identification or comparison.

What is the object of identification in forensic analysis?

To determine the physical or chemical identity with as near absolute certainty as existing analytical techniques permit; testing procedures yield characteristic results for standard materials and results are recorded for repeated use.

What is the second requirement of identification?

The number and type of tests used to identify a substance must be sufficient to exclude all other substances.

What are common types of identification?

Identification of chemical composition of illicit drugs; gasoline residues in fire debris; explosive residues (e.g., dynamite or TNT); identification of blood, semen, hair, or wood.

What is the role of comparison in forensic science?

To determine whether a suspect specimen and a standard/reference specimen have a common origin; both are subjected to the same tests.

What are the two steps in forensic comparison?

(1) Select combinations of properties for comparison; (2) render a conclusion about origins after examination.

What is the role of probability in evidential value?

Probability is the frequency of occurrence of an event; many analytical processes cannot define an exact probability.

What are individual characteristics?

Evidence that can be associated to a common source with an extremely high probability.

Give examples of individual characteristics.

Matching ridge characteristics of fingerprints; random striation markings on bullets or tool marks; irregular wear patterns in tire or footwear impressions.

Additional examples of individual characteristics (handwriting, breaks, bags).

Handwriting characteristics; fitting irregular edges of broken objects like a jigsaw puzzle; matching striation marks on sequentially produced plastic bags.

What are class characteristics?

Evidence associated only with a group; examples include paint, fibers, glass, drugs, and imprints like some shoe or tire patterns.

What are some weaknesses of class evidence?

It is difficult to assign exact or even approximate probabilities to most class evidence; little statistical data exist.

What is a primary goal regarding statistical data in forensics?

To create and update statistical databases for evaluating the significance of class physical evidence.

What is the value of class physical evidence?

It provides corroboration of events with data that are as free of human error and bias as possible.

What is Crossing Over (1 of 3)?

The line between class and individual evidence is difficult to define; it is rare to encounter two indistinguishable items from different sources.

Crossing Over (2 of 3) questions?

How many striations are needed to individualize a tool mark? How many color layers to individualize a paint chip? How many ridge characteristics to individualize a fingerprint? How many handwriting characteristics tie a person to a signature?

Crossing Over (3 of 3) conclusion?

These questions defy simple answers; the task is to find as many characteristics as possible to compare.

Natural vs. evidential limits (1 of 2)

There are practical limits to the properties available for comparison; modern techniques reveal natural variation is almost infinite.

Natural vs. evidential limits (2 of 2)

Distinguishing evidential variation from natural variation is not always easy.

How does the use of physical evidence affect involvement or exoneration?

As the number of different objects linking an individual to a crime scene increases, the likelihood of involvement increases; evidence that differs from standard/reference samples can exonerate.

What forensic databases are mentioned?

IAFIS (Integrated Automated Fingerprint Identification System); CODIS (Combined DNA Index System); GEDmatch genealogy databases; NIBIN (National Integrated Ballistics Information Network); PDQ (Paint Data Query); SICAR (shoeprint image capture and retrieval).