Nature of Evidence Chapter 3
What is Evidence? Anything that proves or disproves something Relevant- pertains to the matter Materiality- tends to prove something
Different Types of Evidence Physical vs. Nonphysical Physical Any object or thing Nonphysical Verbal testimony Someone’s actions during a crime
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
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
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
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
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
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