1. Nature of Evidence
Chapter 3

2. What is Evidence? Anything that proves or disproves something
Relevant- pertains to the matter
Materiality- tends to prove something

3. Different Types of Evidence
Physical vs. Nonphysical
Physical
Any object or thing
Nonphysical
Verbal testimony
Someone’s actions during a crime

4. 2. Real vs. Demonstrative Real Demonstrative
Generated by criminal activity
Found at the crime scene or elsewhere and pertains to the crime
Demonstrative
Created to help explain or clarify real evidence
Generated after the crime
Examples: scale models, charts, graphs

5. 3. Known vs. Unknown Unknown Known
Evidence at a crime scene whose source is unknown
Examples: bullet in body, blood left from perpetrator
Known
Broken glass window
Note: the broken glass under the window in the soil is unknown

6. 4. Individual vs Class Individual Class
Evidence that could have arisen from only one source
Unique!
Example: Fingerprints
Class
Evidence that could have any of several possible sources
Example: fibers from a pair of pants

7. Identification
Process where evidence is put into successively smaller classes of objects
Some pieces of evidence have minutiae (minor details) that allow evidence to be unique and individualized

8. Comparison Compare unknown evidence with known (or exemplar) evidence
See if both contain at least some of the same unique features
Must have no unexplainable differences
then evidence is individual!
Important points about Comparison Tests
No set number of unique points needed
No statistical data for any evidence other than DNA can be supported with the certainty of a conclusion
No scientific validation to prove the individuality of evidence other than DNA

9. Controls Used to make sure that a test gives you accurate results
False positive test
Test that comes out positive when it should be negative
Example: use negative control like part of shirt with no blood and see if it reacts
False negative
Failure of a test to react when it should
Example: use positive control like a known sample of blood to see if substance reacts