› Established “Locard’s Exchange Principle”-
whenever 2 people/objects come into
contact, materials will be exchanged
between them.
› Criminals contacting an object/person 
cross-transfer of evidence.
 You may find something of the criminal on the
victim and vice versa.

Intensity, duration, and nature of the
materials in contact determine the
extent of the transfer.

Ex: Fistfight vs. Brushing past each other

Trace (or Transfer) Evidence- extremely
small but measureable amounts of
physical or biological material found at a
crime scene.

Briefly describe Locard’s principle of
exchange.

Define trace evidence.

As you watch the video clip about finding trace
evidence:
1. Record information about the various methods
and tools used in collecting trace evidence.
2. Identify the examples of trace evidence
discussed in the video.
**Information may appear on future tests/quizzes**

http://www.youtube.com/watch?v=Iy8sm1V0dk0&feature=share&list=CLcjn6SMEg4a8

While watching the video consider the
following question:
› How can trace evidence help solve a
crime?

http://youtu.be/AMmSCXzmxD4

Evidence that (if true) proves an alleged
fact, such as an eyewitness account of a
crime.
Also known as indirect evidence
 Evidence used to imply a fact but not
prove it directly.


Which major category of evidence
(direct or circumstantial) do you think
trace evidence falls under?
Answer the following question in your
notebook:
 Describe how trace evidence can be a
critical element to solving a crime.
Animal/human hair
 Fingerprints
 Soil or plant material (pollen)
 Body fluids such as mucus, semen, saliva,
or blood
 Fiber or debris from clothing
 Paint chips, broken glass, or chemicals
such as drugs or explosives


Individual evidence- narrows a suspect’s
identity down to a SINGLE person or
thing.
› Evidence typically has unique characteristics
that link it to only one person/thing.
 Example: Fingerprints

Class Evidence- narrows an identity to a
group of persons or things.
› Ex: ABO blood type of a sample of blood
found at a crime scene.

Circumstantial evidence can either be
physical or biological in nature.
› Physical evidence Often reduces the number of suspects to a
specific, smaller group of individuals
(exception being fingerprints).
 Fingerprints, footprints/shoeprints, tire
impressions, tool marks, fibers, weapons,
bullets, and shell casings.
› Biological Evidence May make a group of suspects very small, or
reduce it to a likely individual.
 Body fluids, hair, plant parts, natural fibers.