Unit 2: EvidencePlease pick up Unit 2 Packet A!

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Unit 2 Evidence Targets-By the end of this chapter you will be able to:

summarize Locard’s exchange principle identify four examples of trace evidence distinguish between direct and

circumstantial evidence summarize the seven steps of a crime-

scene investigationsketch a crime scene to scale with

measurementsDistinguish between direct and indirect

graphical relationships.

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VocabularyVocabulary

Forensic Science: Fundamentals & Investigations, Chapter 2 4

Principle of ExchangePrinciple of Exchange

Dr. Edmond Locard, director of the world’s first forensic lab (1910, Lyon, France), established the idea of the exchange principle; namely that:

1. When a person comes in contact with an object or another person, a cross-transfer of physical material can occur.

2. Study of the material can determine the nature and duration of the transfer.

Forensic Science: Fundamentals & Investigations, Chapter 2 5

Types of Evidence Types of Evidence

Direct evidence Testimony by a

witness about what that witness saw,

heard, or did

Forensic Science: Fundamentals & Investigations, Chapter 2 6

Types of Evidence Types of Evidence

Circumstantial evidence

• also called Indirect

• trace evidence

Physical evidence

• e.g., fingerprints

Biological evidence

• e.g., blood or hairs

Forensic Science: Fundamentals & Investigations, Chapter 2 7

Types of Evidence Types of Evidence

Class Individual

Identifies group of person/things

Identifies specific person/thing

e.g. Blood Type e.g. fingerprint

Forensic Science: Fundamentals & Investigations, Chapter 2 8

Types of EvidenceTypes of Evidence

Explain why this would be or would not be trace evidence

Types of Evidence

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Documents • Hand written• Type or Printed• Authenticity?

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Glass • How it was broken?• Link a suspect to a crime scene• Fingerprints• Blood

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Soils, Minerals, Wood, and Other Vegetative Matter.

• Location • Link suspect• Trace Evidence

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Fingerprints

• Mainstay of Forensics• Who is on file?

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Hair

• What type?• How removed?• Match to a person• DNA

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Fibers

• Link suspect to a location or victim

• Origin?

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Firearms and Ammunition • Circumstances of discharge• Link to suspect• Link to weapon• Link to victim

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Powder Residue• Evidence of shooting• Circumstances of shooting• Type of weapon

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Explosives & Propellants

• Link to suspect or victim• Origin

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Tool Marks • Match tool to scarsMatch tool to scars

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Impressions

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•Location?•Link to suspect or victim

Drugs • Type of Drug?• Strength?• Origin?• Legal?

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Paint • Origin• Match

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Blood, Semen, Saliva, Organs, & other Physiological Fluids

• Origin• DNA• Condition

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Forensic Science: Fundamentals & Investigations, Chapter 2 24

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

Forensic Science: Fundamentals & Investigations, Chapter 2 25

Crime-Scene Sketch Form

Forensic Science: Fundamentals & Investigations, Chapter 2 26

Crime-Scene Sketch Example

Forensic Science: Fundamentals & Investigations, Chapter 2 27

Analyze the EvidenceAnalyze the Evidence

Lab results can: o Show reliability of witness accountso Establish the identity of suspects or victimso Show suspects to be innocent or link them

with a scene or victim

Forensic Science: Fundamentals & Investigations, Chapter 2 28

. . . . . . . . . . . . . . . . . . . . . . . . . . . . SummarySummary . . . . . . . .

o Locard’s exchange principle: • Contact between people and objects can

transfer material that can determine the nature and duration of the transfer

o Evidence can be direct or indirect • Physical or biological traces

o Investigations consist of recognizing, documenting, and collecting evidence.

Graph Relationships

o When you look for patterns in the data that you have graphed

o There are 2 different patterns you may find:• direct• inverse

Forensic Science: Fundamentals & Investigations, Chapter 2 29

Direct relationship

• Relationship Statement:

When the independent variable is at its highest, the dependent variable is at its highest

Forensic Science: Fundamentals & Investigations, Chapter 2 30

Inverse Relationship

• Relationship Statement:

When the independent variable is at its highest, the dependent variable is at its lowest

What if no relationship is shown?

• If the graph looks like

• Relationship Statement: When the independent variable increases, the dependent variable doesn’t change

What if no relationship is shown?• If the graph looks

like• Relationship

Statement: When the independent variable increases, the dependent variable does not change in a predictable way