there are three categories of tool marks compression tool marks, sliding tool marks, and cutting tool marks. Tool marks are usually used by criminals to gain entry to a premises. Criminals such as my neighbor, whom attempted to force entry in my apartment with a screw driver, often leave behind evidence. Forensic evidence can be the key to solving the crime.
Furthermore, the examination of tool marks, along with other evidence, is based on two characteristics. Class characteristics are characteristics that are common to a group of objects. For example, a crowbar has a distinctive shape and typical size. Individual characteristics are characteristics that are unique to a given object. Tool mark impressions can vary in size and shape depending on the object that was used to force entry.
Tool mark impressions are caused by the interaction of two objects. Impressions can be distinguished in several different ways.
1. Compression or static marks are when a tool is pressed in to a softer material such as a screw driver impression on a piece of wood.
2. Dynamic or sliding marks are made when a tool slides or scratches across a surface. An example of a sliding/dynamic mark is: (My back door).
3. Cutting marks are a result of pressure being applied at both sides of an object and are often associated with scissors etc.
4. Multi-stroke marks are caused by repetitive action such as a saw moving back and fourth.
Last, tool mark examination is conducted when a tool is recovered that is suspected to have caused the damage. If a tool is found on the scene, it is taken to the lab for further analysis. The Forensic Scientist will make test marks using the suspect implement. The test mark and the mark recovered from the crime scene will then be compared. The Forensic Scientist will examine and compare the striation patterns using the comparison microscope. By comparing and matching the striations the scientist can prove whether the tool is responsible for the impression. Tools can also have trace evidence, such as paint flakes adhering, or in the case of a human victim, blood or other body fluids. This evidence greatly assists in the investigation of a crime.
(Nordby)
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