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TOOL MARK IDENTIFICATION

TOOL MARK IDENTIFICATION. Tool. An object used to gain mechanical advantage. Also thought of as the harder of two objects which when brought into contact with each other, results in the softer one being marked . Tool Marks.

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TOOL MARK IDENTIFICATION

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  1. TOOL MARK IDENTIFICATION

  2. Tool An object used to gain mechanical advantage. Also thought of as the harder of two objects which when brought into contact with each other, results in the softer one being marked.

  3. Tool Marks • Any impression, abrasion, or cut made when contact occurs between a tool and an object • Even mass-produced tools have minor differences that can differentiate one tool from another (Recall the differences between class and individual characteristics)

  4. Types of Tool Marks • Indentation Marks: made when a tool is pressed against a softer surface; this mark is a negative impression of the tool; ex: screwdriver on wood • Abrasion Marks: made when surfaces slide across one another; ex: pliers or knives; the harder surface leaves scratch marks or striations on the softer surface • Cutting Marks: produced along the edge as a surface is cut; ex: saw or wire cutters

  5. Tools – Classification • Tools can be classified according to type of action it imparts on the work piece. The action affects the marks left on the work piece. • Examples of different types of actions include: • Compression • Flat Action • Gripping • Shearing • Slicing

  6. Tools - Compression • Compression tools are designed to compress by pressure or impact. These tools include hammers, chisels, and die stamps.

  7. Tools – Flat Action • Flat action tools work in parallel to the working surface. These types of tools include screwdrivers, pry bars and tire irons.

  8. Tools – Gripping Action • These tools use opposing jaws to squeeze or hold an object. Tools in this category include vise grips, tongue and groove pliers, and pipe wrenches. They are also called serrated jaw gripping tools.

  9. Tools - Pinching Action These tools use opposed jaws which are designed to cut using a pinching action. Examples of these types of tools include bolt cutters and diagonal cutters.

  10. Tools – Shearing Action Shearing tools use two blades on adjacent planes that pass by each other and are designed to cut. These types of tools include scissors, tin snips, wire cutters, and pruning shears.

  11. Tools – Slicing Action • Slicing tools cut materials by moving a sharp blade along the direction in which it is traveling. These tools include knives and razors.

  12. Documenting Tool Mark Evidence—Photography • Photograph all the evidence with a measuring device to show appropriate scale for reference • Use oblique lighting because it casts shadows and highlights details that are not easily visible under direct light

  13. Documenting Tool Mark Evidence—Casting • If possible, the piece of wood, metal, etc. that has the tool mark evidence should be removed and kept as evidence • If not possible, a cast impression should be made using silicone or rubber-based casting materials such as Mikrosil • Be sure to dust for prints before making a cast

  14. Test Marks • Several types of tools are tested to see if they can make a similar mark • By comparing the crime scene tool marks with the test marks, the kind of tool used in the crime can be determined

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