Transcript Forensic Evidence

Forensic Evidence
Unit 1
Fresh bacon?
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3rd century China murder
Eureka! – a bit of history
Hint!
D = M/V
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Hiero, king of Syracuse in the third century B.C.,
gave a jeweler a bar of gold and ordered the
jeweler to make it into a crown.
When the jeweler delivered the crown to the king,
the king measured the mass of the crown and
found that the crown had the same mass as the
gold he had given the jeweler.
Even so, Hiero was suspicious. He believed that
the jeweler had cheated him and substituted
some less precious metal for the gold. Hiero
asked Archimedes, a natural philosopher, to find
a way to demonstrate that the crown was not
pure gold.
What is forensic science?
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Forensic Science
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Application of science to help resolve
matters of
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Criminal Law
 2) Civil Law
Federal Rules of Evidence
These rules govern what evidence is admissible
and how it can be used in court.
The evidence must be :
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probative – it must prove something
material – it must be relevant and significant to the crime
*** hearsay is not admissible – it is what others have said being restated by
someone…Gossip!!!!
Scientific Evidence
Two legal decisions have influenced what scientific
evidence is allowed in courts
 The Frye Standard – (1923)
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the scientific evidence must be generally accepted as true
by the community as a whole to be acceptable in the
court of law.
The Daubert Ruling – (1993)
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Scientific evidence is getting to complex so guidelines
were offered
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The scientific theory must be testable
Other experts must be able to review the theory to be sure
it is valid
The rate of error must be given (percentage error)
The technique must follow standards
The court must decide whether the theory has widespread
acceptance inside a specific scientific community
before fingerprints…
How many people are in the video?
Describe the main character(s) in the commercial in terms of:
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Describe the other people in the commercial.
Describe the setting(s) of the commercial (where it was located).
What furniture, if any, was in the commercial?
Was it possible to determine the season?
What were the people doing in the commercial?
Were there any cars in the commercial? If so, describe the:
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Size
Age
Skin color
Height
Weight
Hair: style, color, length
Clothing
Hat
Glasses
Distinguishing features
Jewelry
Beard or no beard
Any physical limitations
Model
Year
Color
How long was the video?
What is the solgan?
What does this say…
Illusions
http://www.pbs.org/wnet/brain/illusio
ns/index.html
 Perceptions are influenced by our
past experiences, imagination, and
associations
 We believe what we see (or think we
see)
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12 angry men old man
Perceptual Fallacies
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Color constancy
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Size constancy
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Phone in the shower
Clarity in vagueness
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Ba Mbuti Tribe
Expectation
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Tree and donkey
Clouds
Constructive Memory
Judging
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Friend called when your thinking of them
2 Types of Evidence
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Testimonial
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A statement made under
oath, such as an
eyewitness testimony
Physical
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An object or material that
is relevant to a crime
(tangible, large or small)
Testimonial Evidence
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Interesting Facts
Jury’s are heavily influenced by
eyewitness accounts
 Most known cases of an innocent person
going to jail are due to a mistaken eye
witness account
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 Innocence
project: 87% of
wrongful convictions due to faulty
eye witness accounts
Reliability of Eye Witness Accounts
Factors that influence reliability
 The type of crime it is and how it was seen by the witness
Serious crime? Weapon involved? Is the witness physically
similar to the suspect? Was it a stressful situation
 Characteristics of the witness
Adult vs. children? Alcohol, drug involvement? Poor eyesight
or hearing? Head injury?
 Manner in which the information is retrieved
Interviewing techniques used? Open ended questions…not
leading questions (ex. ‘did he have any marks on his face
that would suggest he had been in a fight..’)
 Witness’s prior relationship with the accused
Does the witness know the suspect?
 Length of time between the offense and the identification
How long has it been since the crime?
Police Composite
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Composite may be
developed from the
eyewitness testimony
by a computer or
forensic artist
The bottom line in eye
witness testimony is…
“Perception is reality”
Suspect Composite
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You and your partner will be responsible for
reconstructing the face of a person
You will have aprox. 1 minute to observe the
person
Things to focus on:
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Overall shape
Shape of the jaw
eyes, nose, mouth
Facial hair
Piercing
Facial markings
Width of neck
Protrusion of ears
Forehand lines
Nostrils
Methodology of the Forensic Scientist
A fundamental principle of every crime scene studied is…
Locard’s Principle
“Whenever two objects come into contact, there is always
transfer of material.”
The methods of detection may not
be sensitive enough to demonstrate
this, or the decay rate may be so
rapid that all evidence of transfer
had vanished after a given time.
Nonetheless, the transfer has taken
place.
Value of Physical Evidence
Physical Evidence - object or material that is relevant to a crime (tangible, large or small)
 Generally more reliable than testimonial
 remember eyewitness testimonies in 12 angry men
 5th Amendment
 Can prove that a crime has been committed
 example - gasoline at a scene of an arson
 Can corroborate (support) or refute testimony
 can test blood stain to prove the suspects claim it is his own not the
victims
 Can link a suspect with a victim or with a crime scene
 a broken piece of glass found on suspect that matches the headlight of a
hit and run
 Can establish the identity of persons associated with a crime
 fingerprints, DNA, handwriting at the crime scene
 Can allow reconstruction of events of a crime
 what happened, sequence of events
 Provide a powerful interrogation tool
 police can ask better questions knowing specific information
Value of Physical Evidence
• Circumstantial Evidence
•Implies a fact or event without actually proving it
•Examples: a black hair, a size 11 footprint
You hear people classically say “Oh their case is based on purely
circumstantial evidence.” Implying it is not good evidence for the
case.
Physical evidence is circumstantial evidence
Probability and Statistics determine whether the circumstantial evidence is
useful or not
Collecting Physical Evidence
The main goal of the forensic science team is …
to link the victim, suspect, and crime scene with evidence.
Victim
Crime Scene
The Forensic Team
Coroner or Medical Examiner
Law enforcement officials
Forensic scientists
Crime Scene Investigators
Lab technicians
Suspect
Class Evidence vs. Individual Evidence
Class Evidence – common to a group of objects or
persons
•Small broken glass
•Blood type
Only useful if it is
used in
connection with
other evidence!
Fuzzy Line
Individual Evidence – can be identified with a
particular person or a single source
•High probability of linking two pieces of
evidence
•Fingerprints – 1 x 1060
WTHS Theft
Light brown hair
 Shirt with majority black
 Blue jeans
 Dark colored shoes
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