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

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.