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Evidence Chapters 3 & 8. Types of Evidence 2 types exist Testimonial Physical.

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Presentation on theme: "Evidence Chapters 3 & 8. Types of Evidence 2 types exist Testimonial Physical."— Presentation transcript:

1 Evidence Chapters 3 & 8

2 Types of Evidence 2 types exist Testimonial Physical

3 Testimonial Evidence Statement made under oath Known as direct evidence AKA Prima Facie evidence

4 Reliability of Eyewitnesses Factors that can help or hurt your case Nature of the offense and the situation in which the crime is observed Characteristics of the witness Manner in which the information is retrieved Witnesss prior relationship with the accused Length of time between the offense and the identification Any prior identification or failure to identify the defendant Any prior identification of a person other than the defendant by the eyewitness

5 Eyewitness A police composite may be developed from the witness by forensic artist or a computer program As a result of the influences in eyewitness memory, physical evidence becomes critical.

6 Physical Evidence Impossible to list ALL objects that can be found at a crime scene Remember, physical evidence can be ANYTHING

7 Common Types of Physical Evidence Blood Semen Saliva Documents Drugs Explosives Fibers Fingerprints Firearms and ammunition Soil and minerals Vehicle lights Glass Hair Impression Organs Petroleum products Plastic bags Plastic, rubber, and other polymers Powder residue Serial numbers Wood and other vegetative matter

8 Types of Physical Evidence 5 types exist Transient Pattern Conditional Transfer Associative

9 Transient Evidence Is temporary evidence; can be changed or lost; usually observed by the first officer at the scene Examples Odor- perfume, gas, urine, cigarette Temperature- surroundings, coffee, water, dead body Imprints and indentations- footprints, teeth marks, tire marks Markings

10 Pattern Evidence Produced by direct contact between a person and an object or between two objects Examples Blood spatter Glass fracture Fire burn pattern Tire marks Gun powder residue Body position Tool marks Furniture position Projectile trajectory

11 Conditional Evidence Produced by a specific event or action Examples Light- lighting conditions Smoke- color, direction of travel, density, odor Fire- color and direction, speed of spread, temperature and condition of fire Location- injuries or wounds, bloodstain, victims vehicle, weapons, broken glass Vehicles- doors locked or unlocked, windows opened or closed Body- position, types of wounds; rigor, livor, and algor mortis Scene- condition of furniture, doors and windows, signs of struggle

12 Transfer Evidence Produced by contact between person(s) or object(s), or between person(s) and person(s) Examples Fingerprints Hair Fibers

13 Associative Evidence Items that may associate a victim or suspect with a scene Examples Suspect has victims credit card or watch

14 Classification of Evidence by Nature 4 classifications Biological Blood, semen, saliva, sweat, tears, hair Chemical Fibers, glass, soil, gunpowder, metal Physical Fingerprints, footprints, shoe prints, handwriting Miscellaneous Voice analysis, polygraph, vehicle identification

15 Value of Physical Evidence Generally more reliable than testimonial Can prove that a crime has been committed Can corroborate or refute testimony Can link a suspect with a victim or with a crime scene Can establish the identity of persons associated with the crime Can allow reconstruction of events of a crime

16 Forensic Investigations Includes some or all of the seven major activities Recognition- ability to distinguish important evidence from unrelated material Pattern recognition Physical property observation Information analysis Field testing Preservation- collection and proper preservation of evidence

17 Forensic Investigations Identification- use of scientific testing Physical properties Chemical properties Morphological properties Biological properties Comparison- class characteristics are measured against those of known standards or controls; if all measurements are equal, then the two samples may be considered to have come from the same source or origin

18 Forensic Investigations Individualization- demonstrating that the sample is unique, even among members of the same class Interpretation- gives meaning to all the information Reconstruction- reconstructs the events of the case Inductive and deductive logic Statistical data Pattern analysis Results of laboratory analysis

19 Common Types of Identification Crime labs may be requested to identify the following Chemical composition of illicit drugs Gasoline in residues Nature of explosive residues Blood, semen, hair, or wood Blood has to be identified as human vs. other animal

20 Classifying Characteristics 2 types of characteristics Individual Evidence that can be associated with an extremely high degree of probability Example- each gun makes a different impression on the bullet when fired Class Evidence associated only with a group Example- blood types

21 Class vs Individual These fibers are class evidence; there is no way to determine if they came from this garment The large piece of glass fits exactly to the bottle; it is individual evidence

22 Role of Probability Important in ascertaining the origins of 2 or more specimens It is the frequency of occurrence of an event

23 Example- Bad Suppose a crime took place in which the suspect left blood behind. The forensic scientist determined that the suspect has type A blood. Any person brought in and whose blood type was also A cannot be arrested on that ground because over ¼ of the population have that blood type.

24 Example- Good Suppose a crime took place in which the suspect left saliva behind. The forensic scientist did a DNA analysis of the saliva and came up with a match to the actual suspect.

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