READ: Arson, Firearms and Toolmarks

Tool Marks and Impressions

Tool Marks

A tool mark is any impression, scratch, or abrasion made when contact occurs between a tool and an object. Like firearms, tools also have irregular ridges and valleys as a result of manufacturing and/or use. Similarly, observing for striations on tools to compare to marks made at the crime scene can help link a particular tool to a crime scene and possibly a suspect. Some of the most common types of tool marks include abrasion marks, cutting marks, and indentation marks. Abrasion marks are made when one surface slides across another and essentially scratching the surface. Cutting marks are produced along the edge as a surface is cut. Indentation marks are made when a tool is pressed against a softer surface resulting in an impression of the harder tool in the softer material. This can be quite useful in identifying the tool!

Because continued use can change the striations on the tool and because the crime scene evidence could be altered, it is imperative that the tool never be put back in the crime scene mark to see if it matches. Instead a clay or putty casting should be used to mold a pattern of the weapon.

Other Impressions

Other impressions include tire treads, shoe prints, or fabric impressions. Tire treads and shoe prints can be preserved by casting them in plaster. Before casting the impressions should be photographed. Casts can then be collected and stored indefinitely. Fabric impressions can be made in a variety of ways. In fact, fabric impressions can be left behind as a result of a hit and run by the victims' clothing onto the surface of the accident vehicle. The primary consideration in collecting impressions is to preserve the impression or its reproduction for later examination in the crime lab.

Georgia Virtual, Firearms, Ballistics, Toolmarks, and Arson, CC BY-NC-SA 3.0