Tool marks (FSC)

Summary

This module covers the forensic analysis of tool marks, discussing how tool impressions, cuts, or scratches on softer materials help investigators link tools to crimes. It explains the two types of tool marks: impressed and striated, which are caused by varying forces during criminal activities. The module emphasizes the importance of documenting and examining tool marks through photography, sketches, and the use of microscopes to identify unique characteristics. Proper handling of evidence, preservation of microscopic details, and comparison techniques are essential in linking tools to suspects in crime investigations.

Takeaways

• 🔧 Tool marks are impressions left when a harder object contacts a softer one, often used in crime investigations.
• 🔍 These marks can include cuts, stabs, abrasions, scratches, indentations, and compressions, depending on the force applied.
• 🛠 Examples of tool marks include slashed tires, cut wires, severed chains, and forced entry marks on doors or windows.
• 👣 Tool marks can be classified into two types: impressed (compression) marks and striated marks (scraping or abrasion).
• ⚖️ Forensic examination of tool marks can establish a direct link between a specific tool and a crime scene, helping in investigations.
• 🔍 Tool marks are classified into class characteristics (broad features like shape and size) and individual characteristics (microscopic, unique features).
• 🧪 In forensic analysis, tools should never be fitted into tool marks at a crime scene as it can damage the evidence.
• 📸 Proper documentation of tool marks is essential, including photographs, sketches, and notes to accurately capture the scene.
• 🧰 Tools often used in crimes include screwdrivers, hammers, pliers, and cutters, and these can leave marks that are critical to investigations.
• 🧬 Tool marks can help reconstruct crime scenes and link tools, and sometimes suspects, to criminal activities.

Q & A

What are tool marks in forensic science?

Tool marks are impressions or striated marks left on a softer surface when a harder object, such as a tool, comes into contact with it. These marks are often left during criminal activities, such as forced entry or vandalism, and can help link a tool to a crime scene.

What are some common examples of tool marks?

Examples of tool marks include slashed tires by knives, hammer strikes on doors, cut fences or wires, and picked locks. Other examples are extrusions marks found on plastic bags or severed chains.

What are the two main types of tool marks?

The two main types of tool marks are impressed (compression) marks and striated marks. Impressed marks occur when a tool is pressed against a surface without any lateral motion, while striated marks are made when the tool moves across the surface, creating a scraping effect.

How are tool marks classified in forensic science?

Tool marks are classified based on their characteristics. Class characteristics refer to the general type, shape, and dimensions of the mark, which can suggest the type of tool used. Individual characteristics are microscopic irregularities unique to a specific tool due to its wear and use.

How do forensic scientists match a tool to a tool mark?

Forensic scientists compare tool marks found at a crime scene with marks made by a suspect tool using comparison microscopes. If the individual characteristics match, the tool is considered to be the source of the mark.

Why is it important not to fit a tool into an impression at a crime scene?

Fitting a tool into an impression at a crime scene can damage the mark and compromise laboratory analysis. This can result in the loss of crucial evidence needed to identify the tool responsible for the mark.

What precautions should be taken when documenting tool marks at a crime scene?

Tool marks should be carefully photographed, measured, and documented with sketches before any removal or casting. Evidence should not be tampered with, and care should be taken to preserve any latent fingerprints or trace materials around the marks.

How do individual characteristics of a tool develop?

Individual characteristics develop over time as a tool is used, worn, cleaned, or damaged. These microscopic irregularities make each tool unique, allowing forensic scientists to identify a specific tool based on the marks it leaves.

What role do tool marks play in crime scene reconstruction?

Tool marks can help reconstruct the crime scene by showing how entry was made, what tools were used, and the direction of force. They can link the suspect's tool to the crime scene and provide evidence for criminal investigations.

How do forensic scientists handle tool mark evidence in the lab?

In the lab, forensic scientists examine the tool and the marks using comparison microscopes. They document the tool’s dimensions, composition, and any unique imperfections. A cast may be made of the tool mark, and the marks are then compared to tool marks made by the suspect tool to identify a match.