Evidence

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.