A slightly different technique for collecting tool mark impression evidence.

In his textbook, Criminalistics: An Introduction of Forensic Science (9th edition), Saferstein describes a tool mark as any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. Throughout the years many different materials have been utilized both in the field and in the laboratory setting to try to accurately replicate the class and/or individual details inherent in a particular tool mark or tool.

In recent years, the forensic community has utilized polyvinylsiloxane impression materials for obtaining tool mark impressions. These materials have been utilized successfully by the dental profession for many years for crown and bridge impressions, denture impressions, bite mark impressions, and other applications. Advantages of the polyvinylsiloxane materials include ease of use, accuracy, and dimensional stability over time while disadvantages include cost of materials and slow setting times at lower temperatures.

Crime scene investigators are intimately aware of the problems associated with attempts to accurately record tool marks at crime scenes both photographically and otherwise. The location of the tool mark, the surface containing the tool mark, and the characteristics of the tool creating the mark can all affect the investigator’s ability to accurately reproduce the tool mark for future comparison.

The following paragraphs describe a modified technique for obtaining tool mark impressions utilizing polyvinylsiloxane impression material. While the marks utilized for this article were from a door located at the authors’ workplace, the tool mark impression techniques described in this article have been successfully utilized at crime scenes by investigators with the Canyon County Sheriff’s Office Forensic Services Team in Caldwell, Idaho.

Materials needed: See Figure1

A. Orthodontic wax rope: this material is inexpensive, re-usable, and can be obtained from most dentists or dental supply companies.
B. Mizzy silicone emulsion spray: this material is available through most dental supply companies, comes in a 4oz bottle for approximately $17.00, and produces a smooth, accurate, bubble-free surface with all impression materials when properly applied.
C. AccuTrans brown casting silicone-polyvinylsiloxane (75ml tube) with AccuTrans automix dispenser from Coltene-Whaledent: the starter kit with dispensing gun and mixing tips costs approximately $200.00.
D. Fingerprint lift card.