Tool mark poster PDF

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Tool mark poster that was used to present lab work....

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HOW TO ANALYSE TOOL MARKS 

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Tools are often used by criminals, typically to enter a site, which usually leave behind evidence for forensic investigators. Even though two tools of the same kind and manufacturer can look the same, there are often natural differences between them, as well as any differences caused by usage. The differences between two tools is what makes gives them unique tool marks. There are two types of characteristics in tool marks, which are class and individual characteristics. Class characteristics are common to groups of tools, such as chisels that are manufactured to a specific size and shape. Individual characteristics are unique to each given object, typically caused by usage and incidents during manufacturing. Tool marks can be distinguished by the interaction between the object and the second object or surface involved. Static marks are made when a tool is pressed into a softer material and leaves an impression. Dynamic marks are a result of a tool sliding/scratching across a surface. Cutting marks are a result of pressure being applied at both sides of an object, such as scissors and wire cutters. Multi-stroke marks are caused by repetitive action, such as saws being moved back and forth.

IS IT A MATCH?      

If a tool mark is found at a crime scene, the scene examiner will remove the object with the marks for further analysis or make a cast of the marks. When examining these marks, a forensic scientist will typically make test marks using the suspected tool and comparing it with the original marks. Comparison is usually done with a comparison microscope, by comparing and matching striations from the original and test marks. When a comparison of a mark is complete it is important to make sure that there are matching striae. Typically, a match is determined by having three matching striae in two groups or six matching striae in a single group(Nichols,2003). Striae are considered a match when the following features are shown:  Positions of striae relative to a reference point.  Height and width of striations.  Consecutive series of known height and width striae.

REFERENCES: 

Nichols, Ronald. “Consecutive Matching Striations (CMS): Its Definition, Study and Application in the Discipline of Firearms and Tool Mark Identification.” AFTE Journal Vol. 35, No. 3, 2003, pp. 298-306....