Physical Evidence

Impression Evidence

Expolsives

Glass

Examination can determine the chemical composition to identify the type of

explosive used and its origin. Traces of explosives found on a suspect

may be matched to explosives from the scene. Materials used to make an explosive device will be compared to

evidence found in the suspect’s possession.

Tool Marks

Particles found at various crime

scenes (breaking and entering, hit

and run, vandalism, or murder) will be

analyzed to determine its properties, such as color, tint, thickness, density, chemical composition, and

refractive index (RI).

Shoeprint and Tire

Ballistics

Characteristics of ammunition, firearms, and residue are examined to find

matches between suspects and evidence found at a crime scene. Chemical tests can reveal gunshot residue (GSR) on a suspect.

Rifling in a gun barrel causes distinctive marks on fired bullets. The National Integrated Ballistics Identification System (NIBIS) is a database used for ballistic evidence.

Bite Mark

Fingerprints

Hairs and Fibers

There are 3 types of patterns:

arches, loops, and whorls. Other characteristics in a fingerprint called minutia are also identify a suspect or victim.

Skeletal Remains

These may be transferred from a suspect to a victims and vice versa. Hairs can be examined to identify their origin, such as human or animal. Hairs with roots intact can be tested for DNA. Fibers are used to make clothing,

carpeting, and furniture. They may be natural fibers (plants or animals) or synthetic.

Body Fluids and DNA

Locard's Exchange Principle

These are analyzed to determine sex, race, approximate age, and stature.

Blood, semen, saliva, sweat, and urine can be analyzed to provide information about the crime as well as its victim or the suspect.

Chemicals and UV light can be used at a crime scene to find areas with body fluids, which are swabbed, bagged and collected in vials.

DNA can be extracted from almost any tissue-hair, fingernails, bones, teeth, & body fluids. A DNA profile is created and compared to those from suspects or victims. CODIS (Combined DNA Index System) is a FBI database that is used to find matches to unknown DNA samples from a crime scene.

Dr. Edmund Locard established the idea that is the foundation of forensic science today.

When a person comes in contact with an object or another person, a cross-transfer of physical evidence takes place.

The intensity, duration and nature of the materials in contact determine the extent of the transfer.

Paint

The Goal

Physical evidence is any material items that are present at the crime scene or related to the crime.

Class Evidence

Physical and chemical analysis of

paint can indicate it’s class or what type of paint it is (auto, house, nail polish, etc.) Individual characteristics, such as the color, number of layers, chemical composition, or features of paint chips, can be analyzed and used for matching evidence to a suspect.

Forensic scientist work to classify evidence with the goal of placing in the smallest class or individualizing the evidence.

Forensic scientist work to classify evidence.

Class: a group of objects or persons with

characteristic physical evidence common to it. Not linked to a single sourse.

A few examples are soil & fibers.

Individual Evidence

Goal-work to Individualize items

Individual characteristics can be identified as having originated with a particular person or source. Used to

establish individuality.

A few examples include fingerprints and DNA.

What we do....

Forensic Scientist work to classify evidence

Classify- to put into a group

In what ways can we classify the students in this class?

Physical Evidence