ABSTRACT
Impression evidence presents itself in the crime scene in a number of forms. Tool marks, footwear or barefoot impressions, tire marks, and even bite marks routinely appear as evidence and require collection. Beyond documentation by close-up photography, casting is the primary mechanism of recovering impression evidence. The term impression, however, at least in forensics, can be deceiving. Impression evidence includes both three-dimensional (3-D) depressions, such as those found when a shoe leaves a mark in soft dirt, and two-dimensional (2-D) marks, such as those found where a dirty shoe leaves a mark on a solid substrate. Although these 2-D marks are not true impressions, casting techniques are an effective means of recovery. The primary methods of recovering impression evidence that the technician should master are the use of rubberized casting compounds (e.g., silicone and rubber compounds for tool marks), an electrostatic dust lifter (ESDL), plaster and dental-stone casting of both 2- and 3-D impressions, and the use of gelatin and other adhesive lifters.
