Forensic Evidence Unit 1.2. What does this say… Illusions ns/index.html ns/index.html.
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Transcript of Forensic Evidence Unit 1.2. What does this say… Illusions ns/index.html ns/index.html.
Forensic Evidence
Unit 1.2
What does this say…
Illusions
http://www.pbs.org/wnet/brain/illusions/index.html
Perceptions are influenced by our past experiences, imagination, and associations
2 Types of Evidence
TestimonialA statement made under
oath, such as an eyewitness testimony
PhysicalAn object or material that
is relevant to a crime (tangible, large or small)
Testimonial Evidence
Interesting FactsJury’s are heavily influenced by
eyewitness accountsMost known cases of an innocent person
going to jail are due to a mistaken eye witness account
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
“Was the man angry?” “Did you see the speeding car?” 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?
Reliability of Eye Witness Accounts
Perceptual Fallacies
Color constancy Tree and donkey
Size constancy Ba Mbuti Tribe
Expectation Phone in the shower
Clarity in vagueness Clouds
Constructive Memory Judging
Friend called when your thinking of them
Police Composite
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
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: Ears Hair Nose shape Forehead Lips Lines Eyes
Observation/Investigation Activity
Groups of 31 observer2 investigators
Observer looks at picture for 30 seconds
Investigators question to re-create scene
Observers only!
Example questions How many cars were in the intersection?
Across the street, are there any parked cars on the side?
Can you describe at least one of the cars driving through the intersection?
Are there any other potential witnesses?
What was this witness doing? Where was he?
What was the speed limit?
Was there anyone parked in the first parking spot?
Methodology of the Forensic Scientist
A fundamental principle of every crime scene studied is…A fundamental principle of every crime scene studied is…
Locard’s Principle Locard’s Principle
““Whenever two objects come into contact, there is always Whenever two objects come into contact, there is always transfer of material.”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 Value of Physical EvidenceEvidence
Generally more reliable than testimonial remember our eyewitness testimonies in class and the 5th amendment
rights
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
Physical Evidence - object or material that is relevant to a crime (tangible, large or small)
• Circumstantial EvidenceCircumstantial Evidence
•ImpliesImplies a fact or event without actually proving it a fact or event without actually proving it
•Examples: a black hair, a size 11 footprintExamples: 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
Value of Physical Value of Physical EvidenceEvidence
Collecting Physical EvidenceCollecting Physical Evidence
The main goal of the forensic science team is …to link the victim, suspect, and crime scene with evidence.
The Forensic TeamCoroner or Medical ExaminerLaw enforcement officialsForensic scientistsCrime Scene InvestigatorsLab technicians
Victim
Suspect
Crime Scene
Class Evidence vs. Individual EvidenceClass Evidence vs. Individual Evidence
Class Evidence – common to a group of objects or persons
•Small broken glass
•Blood type
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
Only useful if it is used in
connection with other evidence!
Fuzzy Line
WTHS Theft
Light brown hairShirt with majority black Jacket/SweatshirtLight colored shoes
Reading: Anonymity Project
How does this article apply to the locard principle?
Where do you see things in your life that make you easily traceable?
How do you feel about privacy vs. technology, worth the price?
General feeling towards author’s findings