Crime Scene Investigation
and
Evidence Collection
Physical Evidence
• Any and all objects that can establish that can
establish that a crime has or has not been
committed or can link a crime and its victim or
perpetrator
– In order to be useful it must be collected,
preserved and properly analyzed by forensic
experts
– The CSI Myth…Crime laboratories do not solve
crimes yet only enhance the ability of investigators
to solve crimes by providing them with data.
Types of Evidence
Direct vs Circumstantial
Direct
• First hand observations
such as …
– Eyewitness Accounts
– Police Dashboard Cameras
– Surveillance Cameras
• Confessions are also
considered to be Direct
Evidence
Circumstantial
• Indirect evidence that can
be used to imply a fact yet
does not directly prove it
• Provides a link between a
suspect and a crime Scene.
– Can be physical or biological
in nature
Circumstantial Evidence
Physical vs Biological
Physical
• Fingerprints, footprints, shoe
prints, tire impressions, tool
mark impressions, synthetic
fibers, weapons, bullets, shell
casings ect…
• Reduces # of suspects only to
a smaller group of people
– Exception- fingerprints can be
individualized and sometimes
other physical evidence can be
individualized
Biological
• Body fluids (blood, semen,
saliva), hair, natural fibers,
plant part (such as pollen)
ect...
• Usually reduces # of
suspects to smaller group or
even a single individual
– Often more persuasive in
court
Types of Evidence
Class vs Individual
Class
• Evidence that narrows the
identity of a criminal down
to a certain group
(classification) of people
• Does not narrow suspects
down to a single suspect or
criminal.
• Can exclude some suspects
– Example- ABO Blood Type,
Rh+ / Rh – Blood Type, Shoe
size ect…
Individual
• Evidence that narrows the
identity of a criminal down
to a single individual.
– Examples–
• DNA (biological)
• Fingerprints (physical)
• Some other physical
evidence
– Fragments that fit together
like a jigsaw puzzle
• Handwriting *
Types of Evidence
Trace Evidence
• Small but measurable amounts of physical or
biological evidence found at a crime scene
– Examples… write down a few
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Fiber from clothing
Broken glass fragments
Paint chips
fingerprints on glass
Soil on shoes or tracked into a home
Drop of blood on a T shirt
Hair on a brush
Pollen on clothing
Pet hair on clothes or rugs
Locard’s Exchange Principle
• Whenever two people contact with each
other, a physical transfer occurs
• exchange of trace materials/evidence may
occur between two people or a person and
their other environmental surroundings