Forensic Evidence Unit 1.2. What does this say… Illusions ns/index.html ns/index.html.

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Forensic Evidence Unit 1.2

Transcript of Forensic Evidence Unit 1.2. What does this say… Illusions ns/index.html ns/index.html.

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Forensic Evidence

Unit 1.2

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What does this say…

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Illusions

http://www.pbs.org/wnet/brain/illusions/index.html

Perceptions are influenced by our past experiences, imagination, and associations

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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)

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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

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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

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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

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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”

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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

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Observation/Investigation Activity

Groups of 31 observer2 investigators

Observer looks at picture for 30 seconds

Investigators question to re-create scene

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Observers only!

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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?

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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.

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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)

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• 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

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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

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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

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WTHS Theft

Light brown hairShirt with majority black Jacket/SweatshirtLight colored shoes

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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