TOOL MARK IDENTIFICATION
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Transcript of TOOL MARK IDENTIFICATION
TOOL MARK IDENTIFICATION
ToolAn 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 MarksAny 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)
Types of Tool MarksIndentation 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
Tools – ClassificationTools 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
Tools - CompressionCompression tools are
designed to compress by pressure or impact. These tools include hammers, chisels, and die stamps.
Tools – Flat ActionFlat action tools work
in parallel to the working surface. These types of tools include screwdrivers, pry bars and tire irons.
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.
Tools - Pinching ActionThese 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.
Tools – Shearing ActionShearing 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.
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.
Documenting Tool Mark Evidence—PhotographyPhotograph 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
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
Test MarksSeveral 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