Comprehensive Study Guide on Impression Evidence

Impression Evidence

  • Definition: Impression evidence refers to markings left in a soft, malleable material at a crime scene.
  • Common Types:
    • Shoe impressions (also known as footwear impressions)
    • Distinction: A shoe impression indicates a shoe, while a footprint signifies a bare foot (showing toes).
    • Tire track impressions
    • Tool marks
    • Bite marks (with a note regarding DNA as DNA can be associated with bite marks)

Characteristics of Impression Evidence

  • Class Characteristics:

    • Defined as traits that group certain items or individuals together based on shared features.
    • Example: A tread mark from a specific shoe brand, such as Nike or Converse, can be traced back to the manufacturing characteristics of that shoe.
    • Class characteristics include:
      • Shoe brands (Nike, Adidas, etc.)
      • Tire tread patterns (e.g., Goodyear tire model).

  • Individual Characteristics:

    • Defined as unique features that can be attributed to a specific item or individual.
    • Examples include:
    • The unique way a person walks, including wear patterns on shoes.
    • Objects embedded in the shoe impression, such as a pebble that fell into the shoe's tread.

Collection of Impression Evidence

  • Primary Material Used:

    • Dental stone (e.g., TraxStone).
    • Note: Similar to the impression material used in dentistry to create molds of teeth.

  • Collection Process:

    1. Photograph the Impression:
    • Important to include a scale (ruler) for size reference in photographs.
    • Documentation should ensure the size in the photograph corresponds to the actual size of the impression.
    1. Measure the Impression:
    • Measurement is essential for accurate analysis and comparison.
    1. Casting the Impression:
    • Mix TraxStone or similar material until it reaches a consistency similar to pancake batter: not too thick or too thin.
    • Apply the mixture into the impression.
    • Allow time for the casting to harden before lifting it to avoid damage.

Best Practices for Collection

  • Photography Guidelines:

    • Ensure the shoe impression is in clear view and fills the frame.
    • Include the ruler in the shot to establish size.

  • Casting Guidelines:

    • Photograph the entire impression before casting.
    • Assign a placard number to each casting.
    • Aim to capture approximately three feet of a tire track impression for a complete picture of tread.

Examples and Practical Applications

  • Example Types:

    • Various tread marks (include examples from different shoe brands - Fila, Doc Martens, etc.).

  • Field Practice:

    • Suggested equipment for students to practice casting at home (mention of optional purchasing of materials from sources such as Amazon).

Assignments Overview

  • Lab Assignments
    • Focus on comparison of shoe impressions based on photographic evidence.
    • Tasks include:
    1. Comparison lab images
      • Students are directed to download PDF files comparing impressions to known suspect shoes.
    2. Sketching impressions on specific pages of the workbook (Pages 63 & 65).
      • Enhanced methods suggested (using plastic sheet protectors and markers for tracing shoes).

Dates and Deadlines

  • Due Date:
    • Both parts of the lab assignments are due by October 26 for the specified fall semester course.