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Unformatted text preview: Testing Toolmarks Striated The most common tool that leaves striated marks encountered in crime laboratories is a screwdriver. Criminals typically use screwdrivers to try to pry open cash drawers, windows, doors, and car locks. © Precision Forensic Testing Toolmarks Comparisons The striated toolmarks created by flat action tools are reproducible and can be used for comparison between the mark and test marks made by that tool. When making test marks a softer metal is used, typically lead. Lead will not damage the blade during the course of making test marks, yet is hard enough accept the marks. © Precision Forensic Testing Toolmark Comparisons The first step in performing a comparison of striated toolmarks is to establish the correspondence of class characteristics. This will typically be blade width or spacing of the blades if a tool such as a pry bar is used. © Precision Forensic Testing Toolmarks Comparisons After correspondence of the class characteristics has been established, the individual characteristics can be evaluated. We can use these individual characteristics to conclude that the same tool made both marks. © Precision Forensic Testing Toolmarks Striated Another tool that leaves striated marks when contacting a surface is a drill bit. Drill bits cut as they rotate, therefore the striated marks are circular. These striated marks are caused by imperfections on the cutting edge of the blade. © Precision Forensic Testing Toolmarks Striated As with striated toolmarks from bladed tools, striated marks from drill bits can be compared to each other. This is an example of an evidence mark on the left and a test mark made by the suspect drill on the right. © Precision Forensic T...
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- Spring '08