evidence chapters 3 & 8. types of evidence 2 types exist testimonial physical
TRANSCRIPT
Evidence
Chapters 3 & 8
Types of Evidence
2 types existTestimonialPhysical
Testimonial Evidence
Statement made under oath
Known as direct evidenceAKA Prima Facie evidence
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 Witness’s 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
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.
Physical Evidence
Impossible to list ALL objects that can be found at a crime scene
Remember, physical evidence can be ANYTHING
Common Types of Physical Evidence
BloodSemenSalivaDocumentsDrugsExplosivesFibersFingerprintsFirearms and ammunitionSoil and mineralsVehicle lights
GlassHairImpressionOrgansPetroleum productsPlastic bagsPlastic, rubber, and other polymersPowder residueSerial numbersWood and other vegetative matter
Types of Physical Evidence
5 types existTransientPatternConditionalTransferAssociative
Transient Evidence
Is temporary evidence; can be changed or lost; usually observed by the first officer at the sceneExamplesOdor- perfume, gas, urine, cigaretteTemperature- surroundings, coffee, water,
dead body Imprints and indentations- footprints, teeth
marks, tire marksMarkings
Pattern Evidence
Produced by direct contact between a person and an object or between two objectsExamples Blood spatter Glass fracture Fire burn pattern Tire marks Gun powder residue Body position Tool marks Furniture position Projectile trajectory
Conditional EvidenceProduced by a specific event or actionExamples 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, victim’s 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
Transfer Evidence
Produced by contact between person(s) or object(s), or between person(s) and person(s)
ExamplesFingerprintsHair Fibers
Associative Evidence
Items that may associate a victim or suspect with a scene
ExamplesSuspect has victim’s credit card or watch
Classification of Evidence by Nature
4 classificationsBiological
Blood, semen, saliva, sweat, tears, hairChemical
Fibers, glass, soil, gunpowder, metalPhysical
Fingerprints, footprints, shoe prints, handwritingMiscellaneous
Voice analysis, polygraph, vehicle identification
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
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
Forensic Investigations
Identification- use of scientific testingPhysical propertiesChemical propertiesMorphological propertiesBiological 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
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
Common Types of Identification
Crime labs may be requested to identify the followingChemical composition of illicit drugsGasoline in residues Nature of explosive residuesBlood, semen, hair, or wood
Blood has to be identified as human vs. other animal
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 groupExample- blood types
Class vs Individual
These fibers are class evidence; there is no way to determine if they came from this garmentThe large piece of glass fits exactly to the bottle; it is individual evidence
Role of Probability
Important in ascertaining the origins of 2 or more specimens
It is the frequency of occurrence of an event
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.
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.