Toolmarks

Toolmark identification is defined as the identification of any toolmark as having come from a specific tool.

 

Toolmark comparison of marks from a tire punctured with a knife

A toolmark is classified as any impression, cut, gouge, or abrasion caused by a tool coming in contact with a softer object.  The manufacturing process, damage and wear from using a tool result in the production of random microscopic imperfections, or individual characteristics, on the surface of the tool.  When a tool is used on an object, individual characteristics from its surface are reflected in the toolmark left behind at the crime scene.

 

A toolmark examiner produces standards, or test marks made in the laboratory using a suspect tool, to compare to toolmarks recovered from a crime scene.  Standards produced in the laboratory are first compared to each other to determine if the tool is producing individual characteristics in a unique and consistent pattern.  Once a consistently reoccurring pattern is identified on the standards, the standards can then be compared to the evidence to see if the same pattern of marks exists. Comparisons of toolmarks are conducted using a comparison microscope.  A comparison microscope is actually two microscopes joined by an optical bridge, allowing scientists to examine two objects at the same time within the same field of view.  Toolmarks found at the crime scene from screwdrivers, pry bars or other types of tools can be microscopically compared to the test marks in order to identify or eliminate those tools.