Physical Evidence Chapter 3

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What is Physical Evidence?

any and all objects that can establish that a crime has/hasnt been committed or can provide a link between a crime and its victim/crime/perpetrator

If a Investigator doesnt properly preserve or recognize a piece of physical evidence what can happen?

The evidence will be useless, no amount of laboratory instrumentation or technical expertise can salvage the situation.

What can be Physical Evidence?

Almost everything can be physical evidence, its impossible to list all the objects that could be important to a crime.

What is the reason we recognize physical evidence?

So that it can be collected and analyzed.

How much weight does physical evidence have in a case?

There is no clear answer to this, the weight a piece of evidence will have in a case is decided by the jury.

What are some types of Physical Evidence?

• Blood, semen, saliva

• Documents

• Drugs

• Explosives

• Fibers

• Fingerprints

• Firearms and ammunition

• Glass

• Hair

• Impressions

• Organs and physiological fluids

• Paint

• Petroleum products

• Plastic bags

• Plastic, rubber, and other polymers

• Powder residues

• Soil and Minerals

• Tool Marks

• Vehicle lights

• Wood and other vegetative matter

Why is examination of physical evidence done by a forensic scientist?

For identification or comparison purposes.

What is Identification (for physical evidence)?

the determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit.

What occurs in a comparison analysis?

a suspect specimen and a standard/reference specimen to the same tests and examinations for the ultimate purpose of determining whether or not they have common origin.

What is the objective of identification?

Determine the physical or chemical identity with as near absolute certainty as existing analytical techniques will permit.

What does the first step of process of identification require?

First requires the adoption of testing procedures that give characteristic results for specific standard materials. Once these test results are established they may be permanently recorded and used repeatedly to prove the identity of suspect materials.

What is the second step of process of identification?

Second it requires that the number and type of tests needed to identify a substance be sufficient to exclude all other substances.

What is the crime laboratory frequently requested for?

To identify the chemical composition of an illicit drug or a gasoline in residues from the debris of a fire or explosive residues like dynamite or TNT.

What are some very common identification pieces?

blood, semen, hair and wood are very common to determine species origin.

What is comparative analysis´s importance?

Determines whether or not a suspect specimen and a standard/reference and the suspect specimen are subject to the same tests.

What is the two step procedure of forensic comparison?

1. Combinations of select properties are chosen from the suspect and the standard/reference specimen for comparison.

2. Once the examination has been completed, the forensic scientist must be prepared to render a conclusion with respect to the origins.

How is probability connected to comparison?

It brings up a role in ascertaining the origins of two or more specimens. (basically the frequency of occurrence of an event)

How easy is it to establish exact probability?

With many analytical processes its impossible to define (flipping a coin probability is easy to establish in)

What are Individual characteristics?

Evidence that can be associated to a common source with an extremely high degree of probability is said to possess individual characteristics.

Is it possible to state the exactness the probability that the specimens are of common orgin?

It is not possible. Probability is so high as to defy our comprehension or mathematical calculations.

What are class characteristics?

Evidence associated only with a group is said to have class characteristics.

What is a weakness of forensic science currently?

The inability of the examiner to assign exact or even approximate probability values to the comparison of most class physical evidence.

What is one of the primary endeavors of forensic scientists?

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

Can items of physical evidence retrieved at crime scenes be linked to a person or object?

Most cannot be linked definitively.

How much value does class physical evidence have?

Ultimately determined in the courtroom, it lies in its ability to provide corroboration of events with data that are, as nearly as possible, free of human error and bias.

What are the chances of encountering two indistinguishable items of physical evidence at a crime scene that originated from different sources?

Very low.

How can we tell a high certainty that two items came from the same source?

When dealing with more than one type of class evidence, just by their collective presence.

Does crossing over the line from class to individual end the discussions??

It does not

How do natural variations impact modern analytical techniques we use?

Because these techniques are so sophisticated and sensitive natural variaions in o

What are some practical limits that forensic scientists can use for comparison?

• Natural variations to the extreme, that being no two things in this world are alike in every detail.

• Evidential variations being different from natural variations

Is it easy to distinguish variations of evidential to natural?

Not always so easy.

What is the impact of having a lot of physical evidence?

To more number of objects that links a individual to a crime scene increases we increase our chances of the individuals involvement with the crime.

• Not only this but it can help exonerate or exclude someone from suspicion if the samples are different from them.

What is the Integrated Automated Fingerprint Identification System (IAFIS)?

A national fingerprint and criminal history system maintained by the FBI.

What does the Combined DNA Index System (CODIS) do?

enables federal, state, and local crime laboratories to electronically exchange and compare DNA profiles.

What is the National Integrated Ballistics Information Network? (NIBIN)

Allows firearm analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings.

What is the International Forensic Automotive Paint Data Query (PDQ)?

Contains chemical and color information pertaining to original automotive paints.

What is SICAR (shoeprint image capture and retrieval)

is a shoeprint database.