Chapter 3

Physical Evidence

Physical Evidence Any & all objects that:

establish a crime link a crime to its victim link a crime to its perpetrator

Must be recognized at scene & preserved!!

Characteristics of Physical Evidence

Individual Characteristics

Evidence that can be pinpointed to a specific source

Fingerprints, DNA, bullet markings

Class Characteristics

Evidence that can only be associated with a group and not a single source

Fibers, hairs, blood type

Significance of Class Evidence

Unfortunately, most evidence is class so for it to be valuable find as much as possible

As the # of objects , the probability of a person’s involvement

Evidence can also exclude or exonerate an individual

Types of Physical Evidence

1. Blood, Semen, Saliva

Liquid or dried

Human or animal

2. Documents Handwritten or typewritten

Source or authenticity is determined

Clues Type of paper

Ink

Indented writings

3. Drugs Street drugs

(cocaine)

Prescription ones too (painkillers)

Sale, manufacture, distribution, & use

4. Explosives

Any device or object that might contain residues

5. Fibers

Natural (cotton)

Synthetic (nylon)

Locard’s Principle of Exchange

                      

6. Fingerprints

Visible

Plastic

(impression)

Latent (invisible)

7. Firearms/Ammunition

Guns

Bullets discharged or intact

8. Glass

Particles or fragments

Windows with bullet holes

9. Hairs

Animal or human

Species must be determined

10. Impressions Tire marks Shoe prints Tracks Bite marks (food or

skin) Glove & fiber

impressions

11. Paint

Wet or dried

Car accidents or hit-and-runs

12. Powder Residues

From firearm discharge

Check clothing, sheets, & hands

13. Petroleum Products

Oil or grease stains

Gasoline residues

14. Tool Marks

Such as from a hammer that was used in a murder

15. Soil & Minerals Link a person to a

certain location

Often embedded in shoes

Analyzed to tell if a body has been moved

Functions of the Crime Lab

Identification

Determines the physical & chemical properties of a substance

Analytical procedures must eliminate all but one substance

Comparison

Determines whether 2 or more objects have a common origin

Evidence is compared to standard or reference samples

Crime Scene Reconstruction

Pieces together events that occurred before, during, and after a crime

Requires the help of:

law enforcement medical examiner criminalist (forensic scientist)