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Fire Scene Evidence Collection Guide


Toolmark on Substrate

Detailed Procedure:

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.

Toolmarks can be found on any surface, including wood, metal, and soil. Typically, toolmarks are found on door and window frames, lock plates, door locks, door knobs, and ignitable liquid containers. Most often, these substrate materials are at entry points into a structure. The toolmark can be impressed, also called stamped, or striated, also called scraped, or both.

To collect a tool on a substrate:

  1. Photograph the item in place. Toolmarks should be photographed, but photos alone are rarely sufficient for identification of the tool responsible for the mark. Photos are used to establish location, orientation, and size (with an ABFO scale in the photo). Measurements of size and height above the ground should be documented on the scene sketch.

  2. Wear new, unused, clean latex or nitrile gloves.

  3. If possible, collect the full substrate bearing the toolmark. In some cases this may be an object, but in others the substrate may have to be removed from an immovable structure, such as a doorjamb. When collecting a toolmark, be alert for any other evidence that may have been transferred when the mark was made, such as paint or mortar. After photographing, cut any substrate well away from the toolmark so the mark is not obliterated. If needed, tape clean paper over the impression to protect it. Proceed to step 5.

  4. If the item bearing the impression is not recoverable or is likely to be damaged by recovery or transport, it should be cast in a suitable medium. The preferred materials for casting are 2-part forensic casting silicone rubber (such as Mikrosil (TM)), dental impression rubber, or silicone rubber sealant with modeling clay. Mix the medium according to the directions. Apply the medium, being careful not to damage the impression. Allow the casting medium to dry or cure thoroughly before carefully removing it and packaging it for transport.

  5. 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.

  6. Place the item or cast in the container and secure it, if needed.

  7. Seal the container with evidence tape, and initial and date the tape.

  8. 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.

If a tool is not immediately apparent at the scene, consider searching for it. Fruitful locations may be garages, toolsheds, trash receptacles, and vehicles. Be aware that the tool may not have been left at the location and may have been disposed of or still be in the possession of the responsible party. In subsequent searches of any related scenes, include tools in the warrant and search for tools that may have made that mark. Seizure of tools for comparison will result in a more fruitful laboratory examination.

Laboratory testing of toolmarks 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.

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