Tool Marks in Crime Investigation

Tool Marks in Crime Investigation: Understanding and Identification

Tool marks are impressions left by tools on surfaces softer than the tool itself. These marks play a crucial role in crime investigations. They are classified into four types:

1. Impression-type marks: Produced when a tool strikes a surface with pressure.

2. Striated marks: Created when a tool scrapes the surface.

3. Repetitive marks: Result from a tool striking the surface multiple times.

4. Combination marks: A combination of impression and striated marks.

Location and Importance of Tool Marks in Crime Investigation: 

Tool marks often provide vital clues in solving crimes. Class characteristics of a tool mark help identify the type of tool used, while individual characteristics within the marks are unique to the tool itself. These individual traits can include dents, pits, striations, and more, which can be examined under a microscope. Marks from the same tool will have identical individual characteristics.

Criminals frequently employ tools like knives, screwdrivers, or pliers during break-ins or thefts. The tool marks left on locks, doors, or wires can be examined and compared to known tool marks. Additionally, any material adhering to the tool can be analyzed for elemental composition, particle size, and shape using advanced techniques like scanning electron microscopy and spectrographic analysis.

Collection and Documentation of Tool Marks:

When collecting tool marks:

1. Protect the tool marks with cotton.

2. Mark the cut end of items like stolen wires for examination, differentiating them from other ends cut by investigating officers.

3. Do not use the crime tools before forwarding them to the Forensic Science Laboratory.

Techniques for Comparing Tool Marks: 

Comparison of standard and questioned marks is typically done under a comparison microscope. If both marks exhibit similar characteristics, such as a clean-cut appearance and alignment, it can strongly indicate that the same tool created both marks. The comparison involves evaluating the marks' width, arrangement, and overall resemblance. Identical marks are those that closely match under consistent lighting and positioning conditions.