Impression Evidence (lecture 13)

  • Impression Evidence Overview

    • Focus on various types of impression evidence including:
    • Fingerprints:
      • Friction ridges develop pre-birth; unique throughout life (except for scars)
      • Development methods target properties of fingerprint residues
    • Beyond Fingerprints:
      • Other impressions include tongue prints and palm prints
      • Palm prints account for 30% of latent prints at crime scenes
      • Importance of quality prints during booking
    • Footwear Impressions:
      • Often overlooked due to situational factors such as scene contamination
      • Types:
      • 3D impressions (e.g., in mud) require casting
      • 2D prints (on solid surfaces) require photography/lifting

  • Analyzing Footwear Evidence

    • Helps identify or eliminate suspects and confirm alibis
    • Collects data on the crime scene context and number of perpetrators

  • Gait Characteristics

    • Physical characteristics of footprints can vary with activities (e.g., running, walking)
    • Unreliable for personal identification due to variability

  • Evidence Processing Steps

    • Locate footwear evidence with methods like:
    • Electrostatic lifting
    • Chemical development
    • Ensure detailed documentation and recovery of impressions

  • Electrostatic Lifting Devices (ESLD)

    • Effective for lifting 2D impressions; works on dry surfaces
    • Utilizes opposite electrical charges to attract dust particles

  • Casting Impressions Benefits

    • Provides actual size mold of original impressions
    • Captures essential details that photographs may miss

  • Obtaining Known Impressions

    • Gather known impressions from suspects post-crime
    • Important to document and retrieve all footwear from the scene

  • Wear Patterns and Accidental Characteristics

    • Examine wear patterns for potential leads, but cannot solely individualize
    • Accidental characteristics (e.g., cuts, scratches) provide significant identification power

  • Additional Impression Evidence

    • Tire marks and fabric impressions relevant for linking suspects to scenes
    • Bite marks complicate identification but can provide evidence

  • Conclusion: Understanding and properly processing impression evidence is crucial in crime scene investigations for linking suspects and establishing context.