Fire Scene Evidence Collection Guide
Toolmark impressions are made when a hard object deforms a softer material. Toolmark impressions and tools can be affected by heat deformation, water causing rust, corrosion from ash, destruction by fire, and damage from collapse or contact. Toolmark evidence has two parts: a substrate where an impression has been made and a tool that made that impression. In some incidents, these two items may be located in proximity, such as a pry bar dropped outside the door it forced open. In others, only one of the items may be at the scene, most often the impression left by an unknown tool. Laboratory analysis can compare tools and toolmarks to determine if that tool may have made that mark. NEVER fit a suspect tool into a mark at the scene. You may damage the mark or compromise the evidence.
Suspect tools can be used for comparison with toolmarks to determine if that tool could have made the mark in question. Therefore, take care to protect the working surfaces of the tool when collecting it so they are not altered from the state they were found in.
To collect a suspect tool:
Photograph the item in place.
Wear new, unused, clean latex or nitrile gloves.
Label a rigid collection container large enough for the item, such as a box, with identifying information, including case number, date, exhibit number, a brief description, and your name.
Collect the item with gloved hands or other suitable tool, taking care not to touch the working surfaces of the tool or bring them in contact with any other surface. If the working surface is fragile, protect it with an envelope or folded paper secured with tape or a rubber band.
Place the item in the container and secure it (often done with cable ties).
Seal the container with evidence tape. Initial and date the tape.
Store the item in a secure location, such as a locked evidence van or your vehicle, until you are able to transport it to the laboratory.
Laboratory testing of suspect tools may be able to determine:
Laboratory examination comparisons may be on the basis of class characteristics (type, width, shape), individual characteristics (features acquired through use and damage), manufacturer and/or retailers, and "matching" the tool to the toolmark's grooves and features. Tools may contain fingerprints or skin cells (for touch DNA analysis) or other residue (for trace evidence analysis).