forensic science: fundamentals & investigations, chapter 2 1 principle of exchange c.s.i. and...

Forensic Science: Fundamentals & Investigations, Chapter 2 1

C.S.I. and Evidence CollectionPrinciple of Exchange 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


Types of Evidence Types of Evidence

Direct evidence Eyewitness testimony

Videotape (surveillance) Confession



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


Class or Individual

5


Individual Evidence

Really high probability of being

linked to one, unique source

Class Evidence

Object has characteristics common

to a group of similar objects


Types of EvidenceTypes of Evidence

Evidence taken from a crime scene. Direct or circumstantial evidence? ________ Physical or biological evidence? ________ Class or individual evidence? ________


The Crime Scene The Crime Scene Investigation Team Investigation Team

Who is at the crime scene?

Police and possibly a district attorney. Crime scene investigators. Medical examiners. Detectives. Specialists.


The Seven The Seven SS’s of Crime Scene ’s of Crime Scene Investigation Investigation

1. Secure the scene2. Separate the witnesses3. Scan the scene4. Seeing the scene5. Sketch the scene 6. Search for evidence7. Secure the collected evidence


Crime-Scene Sketch Form


Crime-Scene Search Patterns


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


Evidence ID Forms


Chain of Custody

Maintaining a chain of custody log is essential to present credible evidence in court


Chain of Custody (cont’d.)

1. Bag the evidenceAdd identification Seal itSign it across the sealed edge

2. Sign over to a lab technician Open bag on non-sealed edge

3. Return items to the evidence bagSeal evidence bag in another bagSign the evidence log


Analyze the EvidenceAnalyze 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.


Analyze the EvidenceAnalyze 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.


Staged Crime Scenes 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.


Staged Crime ScenesStaged 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?

forensic science: fundamentals & investigations, chapter 2 1 principle of exchange c.s.i. and...

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