Types of Evidence
Chapter 3 Notes
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I CAN Skills for the Physical
Evidence Unit
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I Can review the common types of physical
evidence at crime scenes.
I Can explain the difference between the
identification and comparison of physical
evidence.
I can define and contrast individual and class
characteristic of physical evidence.
I can explain the value of class evidence as it
relates to a crime case.
I can list and explain the function of national
databases available to forensic scientists.
Edmond Locard (1877-1966)
French investigator
Background in medicine and law
1910-started a police laboratory
Founded Institute of Criminalistics at
the University of Lyons
Contributed to fingerprints
(poroscopy)
Locard’s Exchange Principle
1.Principle of cross-transfer
2.Whenever two objects come into
contact there is evidence of that
contact through cross-transfer…
3.Microscopic
4.Macroscopic
Every contact leaves a trace!
PHYSICAL EVIDENCE CAN:
1. Prove that a crime has been committed or establish key
elements of a crime. Example
Rape = victim has torn clothing, bruises, broken arm = nonconsensual
2. Link a suspect with the victim or crime scene
Example : Burglary = suspect has broken glass shards in
his pants cuff that are consistent with glass shards at
scene
3. Establish the identity of persons associated with a crime
Example : Latent fingerprints identified through AFIS. DNA
identified through CODIS.
PHYSICAL EVIDENCE CAN:
4.
Exonerate the innocent. Example : Rape = DNA preserved was
compared against man convicted of the crime = no match.
5.
Corroborate the victim’s story. Example: Officer involved
shootings during arresting a suspect.
6.
Contradict information provided to investigators. Example :
Discredit a witness; elicit a confession
7. Be more reliable than eyewitness testimony.
“[Physical Evidence] does not forget. It is not confused by the
excitement of the moment. It is not absent because human
witnesses are. It is factual evidence. It cannot be wrong; it
cannot perjure itself; it cannot be wholly absent. Only in it’s
interpretation can there be error. Only human failure to find,
study, and understand it can diminish its value.”
Paul Kirk, Crime Investigation, 1953
PHYSICAL EVIDENCE CAN:
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8.
Be the cornerstone of a case. Police/prosecutors
are expected to obtain physical evidence and rarely rely
on a confession alone.
9. And IS expected by a jury/the public. TV, books,
media focus on physical evidence and the miracles
performed (reality vs. fantasy)
10. Support or refute a theory. The absence of forced
entry in a burglary case…
Class and Individual
Characteristics of Evidence
Class characteristics:
Evidence can only be associated with
a group and not a unique source
Individual characteristics:
Evidence can be attributed to a unique
source with a high degree of certainty
(or even to the exclusion of all
others)
Examples of Class
Characteristics
1.
2.
3.
4.
5.
6.
7.
8.
Shoes (Tennis shoe; Nike)
Paint (Cherry red car paint)
Fibers ( polyester fiber, braided weave)
Fingerprints (loops, whorls, arches)
Toolmarks (knife scratch, screwdriver marks)
Firearms (.40 caliber slug)
Arson (accelerants)
DNA (male…remember the sex genes; XY) or
the female XX genes in a genotype of the
blood.
Individual Characteristics of
Evidence at a Crime Scene
1. Shoes (Nike Lunar Vapor 8 Tour Men's
Tennis Shoe, size 7)
2. Paint (physical match with a identified car)
3. Fibers (physical match, unique “trait” of a
particular garmet)
4. Fingerprints (ridge detail enough for
database comparison)
5. Toolmarks (unique stria markings)
6. Firearms (stria matching a test fired bullet,
firing pin markings)
7. DNA (profile that matches the suspect
identically.)
Value of Class Physical Evidence
The value of class evidence lies in its ability to
corroborate events in a manner that is nearly
free of human error and bias. Class evidence is
not as specific as individual, but can produce
results that exclude a suspect.
 As the number of different objects links an
individual to a crime scene.
 A person may be excluded or exonerated from
suspicion if physics evidence collected at a crime
scene is found to be different from the standard
samples taken from the individual. DNA
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Common Types of Physical Evidence
Biological
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Human / animal origins
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–
–
–
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Blood
Saliva
Semen
DNA hair profile.
Physiological fluids
Fingerprints
Hair
Tissues
Bodies
Type of Analysis of Blood, Semen, Saliva,
Organs, & other Physiological Fluids
 Origin
– Comparison to known
suspects or witnesses, victims.
 DNA- Lab analysis to prove who
was there and who was not.
 Condition- samples must be in
good enough condition to be
analyzed. Watch for contamination
with external chemicals / materials.
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Examples of Physical Evidence
being Individual and Proof
1. Pathology wound matches murder
weapon…
2. Glass fragments found in burglar’s
coat pocket…
3. Burglar’s tools…
4. Poison found in suspect’s home
with rare component…
Fingerprints
Mainstay
of Forensics
Who is on file?
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Hair
What
type?
How removed?
Match to a person
DNA
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Impression Crime Scene
Evidence
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Tire Markings – types and sizes of tires, weights
Shoe prints - tread, depth, weight, forces
Depressions in soft soils- Remnants of actions
and activities of numerous people or animals.
All types of tracks- machines, animals, humans.
Material Impressions
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Fabric- gloves, clothing, packs and cases.
Tool marks- hand tools, machine parts, bullet riffling.
Bite marks- human, dog, lions and tigers and bears!
Impact impressions – car lisence plates, bumper
shapes.
– Soils, mud, waste residue.
Impressions
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Tool Marks
Match
tool to scares
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Soils, Minerals, Wood, and
Other Vegetative Matter.
Location
Link
suspect
Trace Evidence
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MANUFACTURED ITEMS
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These are man made items that are very
commonly found at the scene of a crime.
– Weapons of all kinds: Firearms, ammo,
knives, swords, machetes, chainsaws, ropes,
explosives, bombs or components like blasting
caps.
– Polymers, plastic bags, paint, glass, fibers,
petroleum products, vehicle headlights.
– Drugs, chemicals,
– Documents or computer programs.
Firearms and Ammunition
Circumstances
of discharge
Link
to suspect
Link to weapon
Link to victim
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Powder Residue
Evidence
of shooting
Circumstances of shooting
Type of weapon
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Drugs
Type
of Drug?
Strength?
Origin?
Legal?
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Explosives & Propellants
Link
to suspect or victim
by person, place or thing.
Origin; military, civilian?
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Fibers
Link
suspect
to a location
or victim by
direct
comparison
Origin? Type?
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How
Glass
broken?
Link a suspect to a crime
scene
Fingerprints
Blood; type.
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Paint
Origin
Match
Documents
Hand
written
Type or Printed
Authenticity?
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Types of Analysis
Comparison
Visual
Microscopic
Chemical
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Comparison
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Most types of evidence require a
control with which to be compared
http://www.fbi.gov/about-us/cjis/fingerprints_biometrics/iafis/iafis
IDENTIFICATION

Identification has as its purpose the
determination of the physical or chemical
identity of a substance with near certainty in
accuracy.
– Identify the substance and rule out any closely
related substance. Ex. Drugs. Make sure it is cocaine
and not PCP.
– Standards within databases are compared by
computer analysis to help speed things up.
 http://webbook.nist.gov/chemistry/
 http://www.fbi.gov/aboutus/cjis/fingerprints_biometrics/iafis/iafis
Visual Analysis
Evidence utilized through unaided
observation
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Microscopic Analysis
Evidence observed with the use
of some type of microscope
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Chemical Analysis
Evidence subjected
to any type of
chemical procedure
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