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8.29.14
Catalyst:
• Evidence is…
Objectives:
• I will:
– Describe and
differentiate between
the various types of
physical evidence.
– Explain the difference
between class and
individual evidence.
– Properly catagorize
various types of
evidence
"Wherever he steps, whatever he touches, whatever he
leaves even unconsciously, will serve as silent witness
against him. Not only his fingerprints or his footprints, but
his hair, the fibers from his clothes, the glass he breaks, the
tool marks he leaves, the paint he scratches, the blood or
semen he deposits or collects -- all of these and more bear
mute witness against him."
—Dr. Edmond Locard
Physical Evidence
• Physical evidence refers to any material items that would be
present at the crime scene, on the victims, or found in a
suspect’s possession.
• Type of evidence forensic scientists are most interested in
• Forensic scientists will…
– Observe physical evidence
– Determine identity
– Determine origin
What will evidence collected at a scene do for the
investigation?
• May prove that a crime has been
committed
• Establish key elements of a crime
• Link a suspect with a crime scene or a
victim
• Establish the identity of a victim or
suspect
• Corroborate verbal witness testimony
• Exonerate the innocent.
• Give detectives leads to work with in the
case
Common Types of Physical Evidence
Physical evidence…
• Can be any material or object
• Take any form
– Large as a building
– Fleeting as an odor
– Small as a hair
– Microscopic as DNA
• Much more reliable than testimonial evidence
Drug and toxic substance
Resins, plastics
Fingerprints
Paints
Explosive residues
Hair
Gun shot residues (GSR)
Serial numbers
Tissues
Firearms and ammunition Documents
Pollen
Impressions
Fibers
Wood material
Petroleum products
Soil
Feathers
Alcohols (esp. ethanol)
Glass
Bones
Rubber material
Blood and other body
fluids
Tool marks
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Physical evidence…
• Determining origin of a substance almost
always involves a comparison of object or
substance itself with something similar or with
something similar that the scientist knows the
origin of
• Compare with a known or “control”
Trace Evidence
• Trace evidence refers to physical evidence that is found in small but
measurable amounts, such as strands of hair, fibers, or skin cells.
Conditional Evidence
• Produced by a specific action or event at the
scene
• Must be observed and recorded
• Examples
– Lights
– Garage door
– Doors
– Windows
– Position of body
– Position of furniture
Types of Physical Evidence
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Trace Evidence
Transient evidence
Conditional Evidence
Indirect Evidence
Circumstantial Evidence
Individual evidence
Class evidence
Not all evidence is permanent…
• Transient evidence
– Temporary evidence
– Can be easily changed or lost
– Usually observed by first officer on scene and must be recorded at
that time
• Examples?
– Odors
• Perfume, cigarette smoke, gas
– Temperature
• Coffee pot, car hood, water in bath tub, dead body
– Imprints
• Footprints in sand, fingerprints in dust, teeth marks in
perishable food
Indirect Evidence
• Evidence that does not prove or disprove a
fact in question
• Evidence providing only a basis for inference
about a disputed fact
• May prove something like the possession of
controlled substances or driving under the
influence
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Circumstantial Evidence
• Evidence based on suggestion rather than personal
knowledge
• Implies a fact or event without actually proving it
• The more circumstantial evidence there is, the
greater it weighs
• Probability and statistics important
• Examples
– Blonde hair found in hand of murder victim with black hair
– Size 10 sneaker print near the body
– Both of these limit the pool of suspects
Value of Physical Evidence
• Can prove crime has been committed
– Gasoline at a scene of a fire
• Back up witness testimony or disprove it
– Test blood stains of suspects
• Link suspect with victim or crime scene
– Broken glass of headlight in cuff of suspects pants at
scene of hit and run
• Determine identity of people associated with crime
– Fingerprints, DNA
• Allow investigators to reconstruct a crime
– Blood spatter patterns
Individual Evidence
Individual vs. Class Evidence
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Material that can be related to a single source
Individualization always involves a comparison
Narrows an identity to a single person or thing
Examples
– DNA
– Fingerprints
– Handwriting
– Some physical evidence
• Piece of glass that fits another piece like a jigsaw puzzle
Class Evidence
• Material that can be associated with a
group of items that share properties or
characteristics
• Narrows an identity to group of persons or
things
• Examples
– Blue jeans
• We can use some individualization such as
length, style, brand, shade, surface
treatment but there are still thousands of
jeans like that
Class vs. Individual Evidence
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.
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Class vs. Individual Evidence, continued
Draw a concept map of the types of evidence- provide examples
for each; also label each example as class or individual evidence.
Which examples do you think could be
individual evidence?
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