Forensic Science: Fundamentals & Investigations, Chapter 2 1 Principle of Exchange C.S.I. and Evidence Collection Principle of Exchange Established by Dr. Edmond Locard, the principle states: When a person comes in contact with an object or another person, a cross-transfer of physical material can occur Study of the material can determine the nature and duration of the transfer

Forensic Science: Fundamentals & Investigations, Chapter 2 2 Types of Evidence Direct evidence  Eyewitness testimony  Videotape (surveillance)  Confession

Forensic Science: Fundamentals & Investigations, Chapter 2 3 Types of Evidence Circumstantial (indirect) evidence – Used to imply a fact, but does not directly prove it – trace evidence Physical evidence – fingerprints, impressions, bullets, weapons, fibers Biological evidence – body fluids, hair, natural fibers

4 Types of Evidence Class or Individual

5 Types of Evidence Individual Evidence Really high probability of being linked to one, unique source Class Evidence Object has characteristics common to a group of similar objects

Forensic Science: Fundamentals & Investigations, Chapter 2 6 Types of Evidence Evidence taken from a crime scene. Direct or circumstantial evidence? ________ Physical or biological evidence? ________ Class or individual evidence? ________

Forensic Science: Fundamentals & Investigations, Chapter 2 7 The Crime Scene Investigation Team Who is at the crime scene? Police and possibly a district attorney. Crime scene investigators. Medical examiners. Detectives. Specialists.

Forensic Science: Fundamentals & Investigations, Chapter 2 8 The Seven S’s of Crime Scene Investigation 1. Secure the scene 2. Separate the witnesses 3. Scan the scene 4. Seeing the scene 5. Sketch the scene 6. Search for evidence 7. Secure the collected evidence

Forensic Science: Fundamentals & Investigations, Chapter 2 9 Crime-Scene Sketch Form

Forensic Science: Fundamentals & Investigations, Chapter 2 10 Crime-Scene Search Patterns

Forensic Science: Fundamentals & Investigations, Chapter 2 11 Packaging the evidence 1. Crease a clean paper and place evidence in the X position 2. Fold in the left and right sides, and then fold in the top and bottom 3. Put the bindle into a plastic or paper evidence bag affixing a seal over the opening 4. Write your name on the seal

Forensic Science: Fundamentals & Investigations, Chapter 2 12 Evidence ID Forms

Forensic Science: Fundamentals & Investigations, Chapter 2 13 Chain of Custody Maintaining a chain of custody log is essential to present credible evidence in court

Forensic Science: Fundamentals & Investigations, Chapter 2 14 Chain of Custody (cont’d.) 1. Bag the evidence Add identification Seal it Sign it across the sealed edge 2. Sign over to a lab technician Open bag on non-sealed edge 3. Return items to the evidence bag Seal evidence bag in another bag Sign the evidence log

Forensic Science: Fundamentals & Investigations, Chapter 2 15 Analyze the Evidence The facts of the case are determined when the forensic lab processes all the collected evidence. The lab then sends the results to the lead detective who aims to see how it all fits into the crime scenario.

Forensic Science: Fundamentals & Investigations, Chapter 2 16 Analyze the Evidence The lab results can: Show how reliable are any witness accounts. Establish the identity of suspects or victims. Show suspects to be innocent or link them with a scene or victim.

Forensic Science: Fundamentals & Investigations, Chapter 2 17 Staged Crime Scenes When the lab results do not match up with the testimony of witnesses, it can mean the crime was staged; common examples include:  Staging a fire—to cover bankruptcy.  Staging a suicide—to cover a murder.  Staging a burglary—to collect insurance money.

Forensic Science: Fundamentals & Investigations, Chapter 2 18 Staged Crime Scenes Was the crime scene staged? Consider: Does the type of wound match the weapon? Could the wound be easily self-inflicted? What were the mood and actions of the victim before the event? What were the mood and actions of the suspect before the event?