Evidence
2014-2015
Physical Evidence
• Physical Evidence-any and all objects or material
that is relevant in a crime.
– can establish that a crime has or has not been
committed
– can back up witness testimony or prove it false
– can link a suspect to their victim
– can link a person or persons to a crime scene
– can help investigators reconstruct a crime
– May directly prove guilt or may be circumstantial (only
imply guilt).
– In order to be useful it must be collected, preserved
and properly analyzed by forensic experts
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 (Indirect) Evidence
Direct Evidence
Circumstantial or Indirect Evidence
• Prove that some committed
crime
• First hand observations such
as …
• Evidence that can be used to
imply a fact yet does not directly
prove it
– Eyewitness Accounts or
Testimonial evidence
• Generally considered less
reliable
– Police Dashboard Cameras
– Surveillance Cameras
• Confessions are also
considered to be Direct
Evidence
– Is generally physical evidence.
– Provides a link between a
suspect and a crime Scene or
victim.
– The more circumstantial
evidence the greater weight it
carries
Eyewitness Accounts
• Eyewitness Accounts by Victims or Witnesses
• Eyewitness accounts vary considerably from person to
person
• Eyewitness accounts can be unreliable and have led to
the imprisonment of many wrongfully convicted
suspects
» INNOCENCE PROJECT – Project with aim to free
wrongfully convicted
• 87% of all wrongful convictions were a result of
flawed eyewitness testimony
What Effects Our Observations
• Our Brains do not pay attention to all information around us.
• Perception- interpreting information received from our senses
– Perception is skewed by our emotions, state of mind, and prior
experiences or knowledge
• Short term memory – lasts only a short period of time
– A few minutes to 24 hrs
• Long term memory – what is transferred to our memory bank for
long periods
– Days, weeks, months and yrs
Our ability to observe and remember can be
heightened in certain circumstances.
• Example- 911 Attack
• Most people can remember exactly where they were
and what they did on this day.
Types of Evidence
Class vs Individual Evidence
Class
• Evidence that narrows the
identity of a criminal down
to a certain subgroup
(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–
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DNA
Fingerprints
Handwriting***
Some other physical evidence
– Fragments that fit together
like a jigsaw puzzle
» Ransom note torn
from a notepad
– Sometimes impressions
Which examples do you think
could be individual evidence?
Classification of Evidence by Nature
Biological- originating from living things
—blood, semen, saliva, sweat, tears, hair, bone, tissues, urine, feces, animal material, insects,
bacteria, fungi, botanical material
Chemical- can be analyzed for chemical composition
—fibers, glass, soil, gunpowder, metals, minerals, narcotics, drugs, paper, ink, cosmetics, paint,
plastic, lubricants, fertilizer
Physical- a mark or impression that can be analyzed and compared
—fingerprints, footprints, shoeprints, handwriting, firearms, tire marks, toolmarks, typewriting
Miscellaneous
—laundry marks, voice analysis, polygraph, photography, stress evaluation, psycholinguistic
analysis, vehicle identification
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
• There is always a cross transfer of evidence
between a suspect and victim or crime scene
• exchange of trace materials/evidence may
occur between two people or a person and
their other environmental surroundings