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Types of Evidence
Types of Evidence
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Evidence can be divided into two types of
evidence
Direct evidence – evidence in the form of a
statement made under oath, such as a
witness pointing to a person in a court saying
“that’s the guy who robbed the grocery store.”
 Also known as testimonial evidence.
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Types of Evidence
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Evidence can be divided into two types of
evidence
Physical evidence – any object or material
that is relevant in a crime
 Almost any tangible thing, as large as a plane,
as small as hair, as fleeting as an odor, or as
obvious as a demolished building.
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Locard’s principle
Edmond Locard, a French Forensic
Scientitst:
 Always an exchange or transfer of material
when two objects came into contact.
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Types of Common Physical
Evidence
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Drugs and toxic substances
Paints
Gunshot residues
Firearms and ammunition
Impressions (shoes, teeth)
Petroleum products
Alcohols (especially ethanol)
Rubber material
Resins, plastics
Explosive residues
Serial numbers
documents
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fibers,
Soil, glass
Blood
body fluids
Fingerprints
Hair
Tissues
Pollen
Wood material
Feathers
bones
Types of Evidence
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Most evidence does not prove a fact and
is termed indirect evidence. Some
physical evidence, however, may be
considered proof of fact, such as
possessing a controlled substance or a
driver’s blood alcohol level of greater than
0.10%.
Types of Evidence
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Circumstantial evidence – implies a fact or
event. The greater volume of
circumstantial evidence there is, the
greater the weight it carries. Probability
and statistics come into play here.
So, What Good is Evidence?
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Physical evidence can
Prove that a crime has been committed
 Corroborate testimony
 Link a suspect with a victim or with a crime
scene
 Establish the identity of persons associated
with a crime
 Allow reconstruction of events of a crime
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Rules of Evidence
Define what evidence is acceptable
(admissible) and how it can be used for
the jury.
 Evidence must be relevant, meaning it
must prove something (probative) and
address the issue of the particular crime
(material).
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Rules of Evidence
Evidence is admissible if it is reliable and
the presenter of such evidence is credible
and competent.
 Generally, hearsay is inadmissible in
criminal court because it is not reliable nor
was it taken under oath and therefore
does not allow for cross-examination.
Hearsay is admissible in civil suits.
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Two legal decisions
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Legal decisions that govern the
admissibility of scientific evidence:
Frye versus United States, 1923
 Daubert versus Merrell Dow Pharmaceutical,
Inc.
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Frye Standard
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Interpretation of scientific evidence must be
given by an expert witness and have gained
“general acceptance” in the particular field of
study.
The court must decide if the questioned
procedure, technique, and principles are
generally accepted by a meaningful segment of
the relevant scientific community.
Does not offer guidance on reliability.
Daubert ruling
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Trial judge must assume responsibility and
validity of evidence presented in their court.
Guidelines:
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The scientific theory or technique must be testable.
The theory or technique must be subject to peer
review and publication.
Rate of error or potential errors must be stated.
The technique must follow standards.
Consideration must be given as to whether the theory
or technique has attracted widespread acceptance
within a relevant scientific community.
Individual versus Class Evidence
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Individual – best evidence, can be to a single
specific source, so there is no doubt as to what
the source of the evidence is.
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Type of evidence can place a suspect at a crime
scene, associate a suspect with a victim, and
sometimes even prove who committed the crime.
Human characteristics that can be linked to an
individual are fingerprints, DNA analysis, handwriting
voice prints.
Individualization always involves comparison.
Individual versus Class Evidence
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Class evidence is evidence found to be
consistent with a particular source.
Class evidence alone may or may not be very
convincing in a crime, but if there are many
different types or pieces of class evidence, the
value can be considerable.
Class evidence is associated with a group or
class, like polyester or blue polyester shirts.
Examples of class evidence are hair, fibers, soil,
and glass fragments.