Toolmarks in Forensic Investigation

Definition and Scope of Toolmarks

• Definition: A toolmark is any impression, scratch, gouge, cut, or abrasion caused by a tool making contact with another object.
• Context: These marks are frequently discovered at housebreaking crime scenes, often found on wood, metal, and paint surfaces.
• Common Tools: Typical instruments include axes, knives, chisels, crowbars, pliers, and bolt cutters.

Classifications of Tools and Marks

• Tool Categories:     * Flat bladed prying tools: Such as a crowbar.     * Gripping tools: Such as pliers.     * Opposed blade cutting tools: Such as paper cutters.     * Shear cutters: Such as scissors.
• Types of Marks:     * Striated Marks (Kesan Aluran): Result from a hard tool being dragged across a softer surface under pressure (e.g., cutting a padlock).     * Compression Marks (Kesan Tekanan): Created by a hard tool pressed into a softer object without dragging (e.g., a screwdriver pressed into a door frame).     * Variables: The resulting mark is influenced by the angle of the tool relative to the direction of motion.

Crime Scene Examination and Casting

• On-Site Procedures: Investigators must document scratches on paint or metal, photograph marks, and collect physical evidence or suspected tools.
• Integrity Rule: Never test a suspected tool by inserting it into the actual toolmark found at the scene; this must be avoided to prevent contamination.
• Durocast Impression Compound: A putty-like material used to create exact detail castings of toolmarks on both horizontal and vertical surfaces.
• Mixing and Application:     1. Use one level scoop of base material.     2. Flatten and create an indentation in the base material.     3. Add a line of catalyst equal to the length of the indentation and mix.     4. Press the compound into the mark and remove after $8-12\,\text{minutes}$.

Laboratory Analysis and Comparison

• Comparative Analysis: Forensic experts attempt to replicate the exact conditions of the original mark using the suspected tool to create test samples.
• Technical Requirements: Samples must be of similar material and density to the original exhibit.
• Possible Conclusions:     * Positive: The tool is identified as the source of the mark.     * Negative: The tool is excluded as the source.     * Non-conclusive: No definitive link can be established between the tool and the mark.