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Understanding Evidence in Crime Investigations

Jan 16, 2025

Lecture Notes: Types of Evidence in Crime Scene Investigation

Introduction

  • Transition from Chapter 1: Observations and Eyewitness Testimony
  • Focus: Crime Scene Investigation
    • Types of Evidence
    • Limits and Benefits of Different Types

Key Topics

  1. Locard's Principle of Exchange
  2. Examples of Trace Evidence
  3. Direct vs. Circumstantial Evidence
  4. Class and Individual Evidence

Locard's Principle of Exchange

  • Principle: Contact between people/things causes transfer of materials.
  • Examples:
    • Pet hairs: Transfer to clothing, furniture, etc.
    • Hairbrush: Transfers human hairs from the head.
    • Fingerprints: Transfer from fingers to surfaces like glass.
    • Skin cells: Shed and transfer from person to surfaces.
    • Soil: Transfer from shoe to rug, secondary transfer possible.
    • Blood: Transfer between textiles.

Types of Evidence

  • Definition: Anything that helps lead investigators in the right direction.
  • Categories:

    1. Direct Evidence

      • Derived directly from the crime scene or individual.
      • Examples: Eyewitness accounts, video recordings, confessions.

    2. Circumstantial Evidence

      • Indirect evidence that suggests truths but doesn’t prove them.
      • Examples: DNA, fingerprints.
      • Requires more evidence to build a case.
      • Problem: Can link but not always prove.

Class Evidence

  • Definition: Narrows down suspects to a group or class.
  • Examples:
    • Blood type: Rules out individuals not matching the type found at the scene.
    • Tire marks: Links to specific brands/models but not unique.
    • Paint chips: Color and composition narrow suspect pool.
  • Scenario Example:
    • Hair analysis: Blonde hair rules out non-blondes.

Individual Evidence

  • Definition: Unique to one individual, providing strong identification.
  • Examples:
    • DNA: Unique genetic identification (exceptions in identical twins).
    • Fingerprints: Unique patterns for individual identification.

Conclusion

  • Individual Evidence: Valuable for pinpointing one person.
  • End of Video: Questions to be addressed in class.

This lecture emphasized understanding different types of evidence, their roles, and limitations in crime scene investigations. Direct and individual evidence are crucial for proving cases, whereas circumstantial and class evidence help in supporting and narrowing down suspects.

Full transcript