When tools like screwdrivers, pliers, hammers and wire cutters are manufactured, the manufacturing process leaves certain imperfections or patterns, embedded in the tools' surfaces. These patterns are believed to be unique for each tool. This means that when criminals use the tools at a crime scene, to force open a window or to jimmy a door or stab a person in the chest, the toolmarks are often left behind for forensic scientists to analyze.
What are Toolmarks?
Toolmarks are impressions or marks that are produced by a tool or instrument on a receptive surface. When the tool or instrument makes contact with the surface with sufficient force to create an indentation, the pattern of the tool is permanently reproduced onto that surface.
In the world of forensic science, toolmarks can take the form of a negative impression (stamping type) or an abrasion (friction type) mark. Some toolmarks are a combination of both types.
Toolmarks are the Identifying Characteristics of a Specific Tool
Toolmark impressions are usually microscopic and are the result of the imperfections found on the cutting surface of a tool. These marks are the "signature" or identifying characteristics of a specific tool.
Laboratory examinations and comparisons of toolmarks from a “suspect tool“ with toolmarks recovered from a crime scene can often prove conclusive evidence to link a suspect to a specific crime and wrap up the criminal investigation.
Creating a Link Between the Toolmark and the Tool
In a criminal investigation, the goal is to establish a link between a toolmark and the tool that created it at the crime scene. Such links are crucial in forensic sciences, as tools are often used in criminal activities, particularly in burglaries, and can help to identify a criminal. For example, when someone uses a screw driver to force a window open, the marks left by the tool on the window frame are direct evidence of the presence of that tool for that particular use at the crime scene. (Then the tool needs to be matched to its owner).
Evidence Submitted in Toolmark Cases May Include Tools like:
- bolt cutters
- screwdrivers and chisels
- scissors
- knives and box cutters
- pliers and wrenches
- crowbars tire irons
- saws, knives
Places and Surfaces where Toolmarks Might be Observed in Criminal Investigations:
- wire, chains
- door and window frames
- sections of sheet metal
- safety-deposit boxes, safes
- human bone or cartilage
- padlocks, doorknobs
- bolts and locks
- and a variety of other materials.
Toolmarks can be Scratches or Impressions
Toolmarks can be scratches and/or impressions that are left on a surface that is softer than the object or tool that caused the marks. At a crime scene, the unique and individual imperfections on the tool surfaces - that are transferred to the softer surface of the damaged object - can be used to make a positive identification of the tool that may have been used to cause the toolmark striations or impressions.
Minute Scratches - Toolmark Striations
Minute scratches (striations) produced by tests made in the crime laboratory by the questioned tool, will be compared to the striations noted on the evidence toolmark areas.
The forensic scientist (toolmark examiner) using a comparison microscope will conduct comparison examinations to determine whether or not a particular tool may or may not have caused the markings on the evidence from the crime scene.
Impressed Marks - Crowbars, Car Bumpers, Screwdrivers
Impressed marks are also considered to be toolmarks. For example, the tip of a screwdriver or chisel that is used to indent a metal surface but does not penetrate the object will leave an impression that can be identified to that tool.
Other tools like crowbars, hammers and even larger objects like car bumpers or bull bars may leave identifying marks and impressions that, when compared in the crime laboratory, will identify or eliminate the tool or object from the crime scene as being the one that made the impression.
Source:
Missouri State Highway Patrol - Toolmarks
Ames Laboratory (2004, April 14). Using Telltale Toolmarks to Fight Crime. ScienceDaily.
Other Forensic Science Articles:
Karen Lotter - Karen Lotter is a journalist and writer based in Durban, South Africa. She has written profiles, features, advertising copy, ...
