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)