Chapter 2: Types of Evidence

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Chapter 2Types of Evidence

• You can learn a lot by just watching.
• Yogi Berra, former New York Yankees catcher and
  sage

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Evidence
Students will learn

• The difference between indirect and direct
  evidence
• That eyewitness accounts have limitations
• What is meant by physical evidence and give
  examples
• What physical evidence can and cannot prove in
  court
• The significance of individual and class evidence

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Testimonial vs. Physical

• Testimony vs. Physical Evidence

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Eyewitness

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

Facesa composite program by InterQuest
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Reliability of Eyewitness Accounts

• Factors
• 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 relationship with the accused/victim
• Length of time between the offense and the
  identification
• Any prior identification or failure to identify
  the individual or iitem
• Any prior identification of a person other than
  the defendant by the eyewitness

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Types of Evidence

• Two general types
• Testimoniala statement made under oath also
  known as direct evidence or Prima Facie evidence
• Physicalany object or material that is relevant
  in a crime also known as real evidence. Examples
  are hair, fiber, fingerprints, documents, blood,
  soil, drugs, tool marks, impressions, glass.

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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 a crime
• Can allow reconstruction of events of a crime

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Reconstruction

• Physical Evidence is used to answer questions
  about
• What, where, when, how crime took place
• People involved
• Sequence of events

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Types of Physical Evidence

• Transienttemporary easily changed or lost
  usually observed by the first officer at the
  scene
• Patternoften produced by direct contact between
  a person and an object or between two objects
• Conditionalproduced by a specific event or
  action important in crime scene reconstruction
  and in determining the set of circumstances or
  sequence within a particular event
• Transferoften produced by contact between
  person(s) or object(s), or between person(s) and
  person(s)
• Associativeitems that may associate a victim or
  suspect with a scene or each other ie, personal
  belongings

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Examples of Transient Evidence

• Odorputrefaction, perfume, gasoline, urine,
  burning, explosives, cigarette or cigar smoke
• Temperaturesurroundings, car hood, coffee, water
  in a bathtub, cadaver
• Imprints and indentationsfootprints, teeth marks
  in perishable foods, tire marks on certain
  surfaces

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Examples of Pattern Evidence

• Most are in the form of imprints, indentations,
  striations, markings, fractures or deposits.

• Clothing or article distribution
• Gun powder residue
• Material damage
• Body position
• Tool marks
• Modus operandi

• Blood spatter
• Glass fracture
• Fire burn pattern
• Furniture position
• Projectile trajectory
• Tire marks or skid marks

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Examples of Conditional Evidence

• Lightheadlight, lighting conditions
• Smokecolor, direction of travel, density, odor
• Firecolor and direction of the flames, speed of
  spread, temperature and condition of fire
• Locationof injuries or wounds, of bloodstains,
  of the victims vehicle, of weapons or cartridge
  cases, of broken glass

• Vehiclesdoors locked or unlocked, windows opened
  or closed, radio off or on (station), odometer
  mileage
• Bodyposition, types of wounds rigor, livor and
  algor mortis
• Scenecondition of furniture, doors and windows,
  any disturbance or signs of a struggle

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Classification ofEvidence by Nature

• Biologicalblood, semen, saliva, sweat, tears,
  hair, bone, tissues, urine, feces, animal
  material, insects, bacterial, fungal, botanical
• Chemicalfibers, glass, soil, gunpowder, metal,
  mineral, narcotics, drugs, paper, ink, cosmetics,
  paint, plastic, lubricants, fertilizer
• Physicalfingerprints, footprints, shoe prints,
  handwriting, firearms, tire marks, tool marks,
  typewriting
• Miscellaneouslaundry marks, voice analysis,
  polygraph, photography, stress evaluation,
  psycholinguistic analysis, vehicle identification

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Evidence Characteristics

• Classcommon to a group of objects or persons
• Individualcan be identified with a particular
  person or a single source

Blood DNA Typing
Fingerprints
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Class vs Individual Evidence
Which examples do you think could be individual
evidence?
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Class vs Individual Evidence

• These fibers are class evidencethere are
  millions like them.

• The large piece of glass fits to the bottleit is
  individual evidence

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Statistical Significance

• Class evidence can clearly EXCLUDE
• Probative value for INCLUSION increases by
  considering more class evidence
• PRODUCT RULE
• The combined probability of independent events is
  the product of the individual probabilities.

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Statistical Significance

• When flipping a coin once, the probability of
  getting tails is
• ½ or .50 or 50
• When flipping a coin twice the probability of
  getting tails twice is
• ½ x ½ ¼ or .5 x .5 .25 or 25

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Stats in Forensics

• The decision makers must be given an idea of the
  significance of the scientific findingis it
  common or rare?
• The probability of independent events all
  occurring is the product of the probabilities of
  each of the events occurring.
• Used in blood-grouping, DNA typing, etc.

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DO YOUR OWN STATISTICAL ANALYSIS

• Use your class as a representative sample of the
  school.
• Determine the of each observed feature in your
  sample population.
• Count how many of you possess the feature and
  divide by the total in the class.
• Multiply all of the s together.
• This gives you the of people that possess all
  features.
• Multiply the total population of the school by
  the s determined by examining your class.
• This will give you the number of people in your
  school that are likely to possess all of the
  features.

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Forensic Investigations

• Include some or all of these seven major
  activities
• 1. Recognitionability to distinguish important
  evidence from unrelated material
• Pattern recognition
• Physical property observation
• Information analysis
• Field testing
• 2. Preservationcollection and proper
  preservation of evidence

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Investigations

• 3. Identification/characterizationuse of
  scientific testing of properties
• Physical
• Chemical
• Structural
• Biological
• Immunological
• 4. Comparisonclass 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.

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Investigations

• 5. Individualizationdemonstrating that the
  sample is unique, even among members of the same
  class
• 6. Interpretationgives meaning to all the
  information
• 7. Reconstructionreconstructs the events of the
  case
• Inductive and deductive logic
• Statistical data
• Pattern analysis
• Results of laboratory analysis
• Lee, Dr. Henry. Famous Crimes, 2001

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Known and Questioned Samples

• Scientists frequently compare
• QUESTIONED or unknown samples (Q)
• Material collected from a known location but of
  unknown origin
• to
• KNOWN or control samples (K)
• Material that comes from a known or proven source

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The Goal of Analysis

• To identify the source of the evidence
• To determine if there are links between victim,
  crime scene, and suspect
• To reconstruct the crime

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FBI Investigation

• Try a case that was set up by the FBI. Observe
  the various units of their lab and read the
  section How Did They Do That?.
• www.fbi.gov/kids/6th12th/investigates/investigates
  .htm