Physical Evidence
Chapter 3
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Physical Evidence
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Blood, Semen, Saliva
Documents
Drugs
Explosives
Fibers
Fingerprints
Firearms and Ammunition
Glass
Hair
Impressions
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Physical Evidence
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Organs and Physiological Fluids
Paint
Serial Numbers
Tool Marks
Other
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Types of Evidence
 Probative: any item/fact that can prove a
connection to someone or something in case
 Prejudicial: any fact, item or suggestion that
pertains to a previous incident that will bias
jury
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Physical Evidence
 Identification - Determination of physical or chemical
identity of a substance with as near absolute certainty as
the analytical method will permit.
– What is the material? How certain is the answer? What
analytical method(s) will give the best answer (multiple
methods)?
 Comparison - Compares standard and suspect samples to
determine if they have a common origin.
– Can the source of the sample be identified? How
certain is the correlation? How many “data points” are
necessary to be “certain beyond a reasonable doubt” of
the answer (probability)?
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Identification - Determination of the
physical and chemical identity of a substance
with as near absolute certainty as existing
analytical techniques will permit.
 Examples: drug analysis,
species determination &
explosive residue that
contain dynamite.
 Example: Gas
Chromatography / Mass
Spectrometry (GC/MS).
Accurate identification of
a compound.
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Comparisons
 Analysis of a suspect specimen WRT
a standard/reference (exemplar)
specimen to determine whether or not
they have a common origin.
Common
Origin?
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Physical Evidence
 Class (Group) Characteristics - Properties of
evidence that can only be associated with a
general group and not with a common source.
e.g., blood type, paint or dye lot, etc.
 Individual Characteristics - Properties of
evidence that can connect a sample and
standard to a common source (with high
probability). e.g., fingerprints, unusual wear
patterns, tool marks, etc.
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Physical Evidence
 Class (Group) Characteristics - Properties of evidence
that can only be associated with a general group and not
with a common source. e.g., blood type, paint or dye lot,
etc.
Blood Types
World:
Type A - 42%
Type B - 8%
Type O - 47%
Type AB - 3%
“Bodies of Evidence” Brian Innes
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US:
Type A - 39%
Type B - 13%
Type O - 43%
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Type ABCHE
- 5%
Class Characteristics
Where is Waldo?
• Properties of
evidence that
can only be
associated
with a group
and never with
a single
source.
• Can be used to
exculpate a
suspect.
• Examples:
single-layer
paint chip,
blood, nylon
fiber from a
sweater
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Physical Evidence
 Class (Group) Characteristics - Properties of
evidence that can only be associated with a
general group and not with a common source.
e.g., blood type, paint or dye lot, etc.
 Individual Characteristics - Properties of
evidence that can connect a sample and
standard to a common source (with high
probability). e.g., fingerprints, unusual wear
patterns, tool marks, etc.
Example: from “My Cousin Vinny” (20th Century Fox)
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Physical Evidence
 Class (Group) Characteristics - Properties of evidence
that can only be associated with a general group and
not with a common source. e.g., blood type, paint or
dye lot, etc.
 Example: from “My Cousin Vinny” (20th Century Fox)
– 2 people charged with murder during a robbery at a
convenience store (“Sack-O-Suds”).
– Escaped in an older car and skidded tires while leaving.
– Witnesses confused but say they saw the two defendants.
– Expert from FBI called to match tire skids with
defendants car.
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Use of Class Evidence
Effect of “Scientific Expert” on
Jury
Right to have “counter experts”
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Advantages of Class Physical Evidence
Provides corroboration of events based on objective
scientific data
The chances of encountering 2 indistinguishable items of
class evidence that originated from different sources are
variable.
Multiple types of class evidence may lead to an extremely
high chance that they originated from the same source.
Physical evidence has great weight in the courtroom.
Class evidence may also serve to exonerate a person.
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Advantages of Class Physical Evidence
Multiple types of class evidence may lead to an extremely
high chance that they originated from the same source.
Type AB blood - 3%
Rh Negative - 16%
Left-handed - 13%
Male - 50%
Blood Types
World:
Type A - 42%
Type B - 8%
Type O - 47%
Type AB - 3%
Probability for random match =
0.03 x 0.16 x 0.13 x 0.50 =
0.00031 or ca. 3 in 10,000
US:
Type A - 39%
Type B - 13%
Type O - 43%
Type ABCHE- 5%
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Advantages of Class Physical Evidence
Multiple types of class evidence may lead to an extremely
high chance that they originated from the same source.
Type AB blood = 3%
Rh Negative = 16%
Left-handed = 13%
Male = 50%
And Red Haired = 3%
And Over 6’2” = 5%
Probability for random match =
0.03 x 0.16 x 0.13 x 0.50 x 0.03 x 0.05 =
0.00000047 or ca. 5 in 10 million
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Disdvantages of Class Physical Evidence
Next Film Clip Shows Many Impt. Ideas about evidence:
Disadvantages of Class Evidence (especially for
mass produced popular items).
Expert Qualifications
How Class Evidence may be turned into individual
evidence.
QuickTime™ and a
DV/DVCPRO
- NTSC decompressor
Weight accorded
by
juries
to scientific evidence
are needed to see this picture.
Voir Dire - “speaking the truth” - challenging potential
jurors and expert witnesses’ qualifications
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How Class Evidence may be
turned into individual evidence.
My Cousin Vinny conclusion
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Physical Evidence
 Individual Characteristics - Properties of evidence that
can connect a sample and standard to a common source
(with high probability). e.g., fingerprints, unusual wear
patterns, tool marks, etc.
Body of a woman was found
with a knife wound in her
neck. A broken knife tip was
found in the wound. The
knife blade tip was compared
with the knife found in the
husbands pocket. Matches
both in brake line and
scratches.
Saferstein Fig. 3.1
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Individual Characteristics
Firearms ID
 Properties of evidence
that can be attributed
to a common source
with an extremely
high degree of
certainty
 Examples: bullets,
knives, shattered
headlight
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Physical Evidence
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Physical
Evidence
Lindberg Kidnapping Case
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Lindberg Kidnapping
 Chas. A. Lindberg -
first to fly solo across
Atlantic (1927).
 One of the most
famous Americans in
the ‘20’s and ‘30’s.
 June 22, 1930, Chas.
Lindberg Jr. born:
Mar. 1, 1932 he was
kidnapped.
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Lindberg Kidnapping
 Ladder Used in Abduction
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Crime-Scene Reconstruction
 Collaborative effort of law
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enforcement personnel, medical
examiners and criminalists
Was there more than one person
involved?
How was the crime committed?
Reconstruction supports likely
sequence of events by the
observation and evaluation of
physical evidence and statements
made by witnesses and those
involved with the incident
Reconstructions can play a vital role
in aiding the jury to arrive at an
appropriate verdict.
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Crime-Scene Reconstruction
Step 1 - State problem - type of crime and the legal elements.
Step 2 - Collect data - - records checks and police checks,
interview victim, witnesses, and suspects, try to get additional
witnesses and comparison samples from suspects
Step 3 - Form a hypothesis - look at all evidence - determine
motive and possible suspects
Step 4 - Test hypotheses - evaluate how truthful and reliable
the stories are, weigh their stories against the physical evidence
Step 5 - Follow up the most promising hypotheses (theories)
Step 6 -- Draw conclusions - supported by court-admissible
evidence leading to the arrest, prosecution, and conviction of
the offender.
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Homicide:
Rape:
Robbery:
Burglary:
1- focus on deceased 1- focus on victim 1 - modus operandi 1 - focus on scene
2 -crime scene
2 - medical reports 2 - crime scene
2 - records check
3 - crime lab
3 - crime scene
3 - police records
3 - property check
4 - usual suspects
Source: adapted from Gilbert, J. (1980) Criminal Investigation. Columbus: Merrill.
Patterns -- series of similarities that indicate the same person
or the same modus operandi is involved in different crimes.
Leads -- clues or breaks in the case that move an investigation
forward.
Tips -- provided by informants. Tips by definition involve
specifics.
Theories -- beliefs that point in one direction, at the exclusion
of other possible directions.
Clues -- pieces of evidence that are consistent with the corpus
delecti or elements of the crime.
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Physical Evidence
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Crime-Scene Reconstruction
Saferstein “Criminalistics”
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Kennedy Assassination
PETER JENNINGS REPORTING:
THE KENNEDY ASSASSINATION:
BEYOND CONSPIRACY
ABC News Special (Nov. 2003)
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4th Amendment and Evidence
Collection
What does the 4th Amendment to the
US Constitution guarantee?
When would the 4th Amendment
not be applicable?
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