Evidence Collection and Crime Scene Investigation

Objective: Differentiate between the different types of evidence

Do Now: Is blood evidence 100% conclusive?

Locard’s Exchange Principle

“When a person comes into contact with an object or another person, a cross-transfer of physical evidence can occur.”

Types of Evidence

Types of Evidence1. Direct: firsthand

observations (eyewitness account, video camera, confessions) shows that something is a fact without inference or presumption

Types of Evidence2. Circumstantial: indirect evidence;

implies a fact, but does not directly prove it requires making an inference

Trace Evidence:a) Physical – bullets, weapons,

impressionsb) Biological – body fluids, plant parts,

hair

Trace EvidenceSmall but measurable amounts of physical or biological material found at a crime scene

Examples of Trace Evidence

HairFibersSoilfingerprints

Body fluids (semen, blood, saliva, mucus)Paint chipsBroken glassChemical residue

Categories of EvidenceClass Evidence

Narrows identity to a group of persons or thingsExample: blood type

Individual EvidenceNarrow identity to a single person or thingExample: fingerprint

Your TaskIn your groups complete “Identifying types of evidence” activity.

ClosureIdentify what evidence you can collect at this scene State whether its biological or physical then state if its class or individual.

Objective: Problems with evidence collection• Do Now: Can you

convict someone on circumstantial evidence alone?

Case StudyComplete the case study on OJ SimpsonClosure: Do you agree or disagree with the OJ verdict?

Objective: Observe Locard’s Principle Do Now: What led to OJ Simpsons acquittal?

Complete the locard’s principle lab in your groups. Closure: Explain locard’s principle to me as if I was absent and didn’t know it.

Objective: how to process a crime scene

Do Now: What was most useful in analyzing your data in your lab?

The Crime Scene Investigation Team

Who is at the crime scene? Police and possibly a district attorney. Crime scene investigators. Medical examiners. Detectives. Specialists.

The Seven S’s of Crime Scene Investigation

1. Secure the scene. 2. Separate the witnesses. 3. Scan the scene. 4. See that photos are taken. 5. Sketch the scene. 6. Search for evidence. 7. Secure the collected evidence.

1. Secure the Scene

2. Separate the Witnesses

Do not allow witnesses to talk to each otherWitness accounts will be comparedAvoid witnesses working together to create a storyAsked: who, what, where?

3. Scan the sceneDetermine primary and secondary crime scenes

Primary: where murder took placeSecondary: where corpse was found

Where should photos be taken?Wear protective gear to prevent contamination of crime scene

Marking Evidence

4. See that photos are taken

Show the scene exactly as it was when you first saw itIf something was moved before you arrived, don’t try to reconstruct the scene – just take the pictures the way you see itBe careful not to destroy any evidence while taking photos

Overall Shots – Outside the Scene

Exit (door)

First shot entering door:

Outside science office

Overall Shots – Inside the Scene

Overall Shots – Outside the Scene

Exit (door)

First shot entering door:

Outside science office

Overall Shots – Inside the Scene

Evidence: Knife (possible weapon)

Midrange Photo Close-Up (with ruler)

5. Sketch the Crime Scene

Make accurate rough sketchNote direction (N) and scale of distanceInclude relevant objects (body, doors, windows, furniture, immovable landmarks)Make final copy for court

Rough sketch

Final Sketch

6. Search for evidenceGrid, strip or lane, spiral search patternUse flashlight to find hair and fibersUse forceps, vacuum cleaner to collect evidence

Grid Strip or Lane Spiral

7. Secure the Evidence

Properly package, seal, and label ALL evidence!Liquid: airtight, unbreakable containersWet items (biological): dry out in breathable containerDry item: bindle plastic or paper containerSeal with tape and labeled with pertinent info

The Chain of CustodyIn order to present credible

evidence in court, a chain of custody log is essential. (in real life there is more involved but for this class do as follows)

Bag evidence (seal, sign and date)Fill out evidence log every time you open it.

Rough Sketch QuestionsUsing the rough sketch

complete the questions.

Objective: Sketch a crime scene

DO NOW: What happens if the chain of custody is broken for a piece of evidence?

Lab Sketching the Crime Scene

In your groups complete the lab on sketching the crime scene.Divide up the work. Have some members:

1. Take measurements2. Sketch