The Nature of Evidence

Transcription

1 The Nature of Evidence Chapter 3 Mrs. Svedstrup

2 What is Evidence? Legal definition: That which tends to support something or show that something is the case Relevance of evidence- admissibility of evidence Materiality- evidence that tends to prove something Forensic science definition- anything that would make an issue more or less likely than it would be without the evidence Everyday definition- anything that tends to prove or disprove something

3 Types of Evidence Physical-nonphysical Real-demonstrative Known-unknown Individual-class

4 Types of Evidence Physical evidence- consists of objects or things Non-physical evidence- verbal testimony about a crime or someone s actions during a crime

5 Types of Evidence Real evidence- generated be criminal activity. Found at crime scene or obtained from suspectgun, drugs, blood Demonstrative- created to help explain or clarify real evidence- 3-D scale, drawing, charts from analytical instrument

6 Types of Evidence Known evidence- We know where evidence came from and its source (Important during reconstruction of crime scene) Unknown evidence- evidence of which the source is unknown; Bullet found in body is unknown evidence, glass in shoes, blood at crime scene

7 Types of Evidence Individual evidence- a sufficient quantity of characteristics specific to a piece of evidence that allows inference it came from one source, (fingerprint) Class evidence- characteristics of evidence that allow the inference the evidence may have come from several sources (Carpet fiber)

8 Identification Process whereby evidence is put into successively smaller classes of objects Identification of evidence may go through several stages- visual analysis, microscopic, chemical or other testing, etc In fingerprints, patterns and minutiae are used

9 Individual Evidence Evidence Type Fingerprints Handwriting Bullets and Casing Shoe Prints/Tire treads Large pieces of class or paper DNA Individualizing test Compare minutiae Compare known handwriting Compare with markings on knowns Compare details with knowns Fracture or tear match comparison Probabilities of chance occurrence

10 Class Evidence Tiny glass/paint fragments Soils Hairs and fibers Illicit drugs Fire residues Too small to facture match, no unique characteristics Variability vertically and horizontally Hair can be DNA typed, otherwise no unique characteristics in hairs and fibers Drug and contaminants identifiable, but source specificity difficult Can identify residue class (gasoline) but not pump or can gas came from previously

11 Comparison Comparison tests are what determine if evidence is individual Unknown evidence is compared with known evidence There must be a sufficient number of unique points present for evidence identification Examiner must have enough points to be sure his or her conclusion provides that the unknown and known have a common source

12 Comparison There is no statistical data for any evidence types that support a certainty of a conclusion with the exception of DNA There has been no rigorous, scientific validation of principles that underlie the conclusions of individuality of evidence except for DNA

13 DNA Typing Considered to be individual evidence DNA may be associated with one person using quantitative data Genomic DNA typing allows for comparisons between known and unknown DNA Commonality of DNA in population is reliable

14 Controls Test a piece of evidence for certain properties or characteristics, such as blood False positives are positive results when the test should be negative Negative controls are substances that is a known substance or material that would be expected to yield a negative result to a particular test

15 Controls False negatives are negative results that should signify a positive result Positive control- substance that is expected to respond positively to the test Results of false positives or false negatives can have a substantial impact on cases and defendants

16 Evidence Is found at crime scenes Is collected Is compared to known evidence Undergoes identification whereby physical and chemical characteristics can be compared with known evidence and identified as class or individual evidence