Forensic Evidence Unit 1.2

What does this say…

Illusions ns/index.html ns/index.html Perceptions are influenced by our past experiences, imagination, and associations

2 Types of Evidence Testimonial A statement made under oath, such as an eyewitness testimony Physical An object or material that is relevant to a crime (tangible, large or small)

Testimonial Evidence 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

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 3 1 observer 2 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… 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  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 Evidence Circumstantial Evidence Implies a fact or event without actually proving itImplies 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 Evidence

Collecting Physical Evidence The main goal of the forensic science team is … to link the victim, suspect, and crime scene with evidence. The Forensic Team Coroner or Medical Examiner Law enforcement officials Forensic scientists Crime Scene Investigators Lab technicians Victim Suspect Crime Scene

Class 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 Only useful if it is used in connection with other evidence! Fuzzy Line

WTHS Theft Light brown hair Shirt with majority black Jacket/Sweatshirt Light 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