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Tool Mark Analysis (Crime Fighters: Station 1)

Tool-mark analyses help forensic scientists identify the tool or tools used at the scene of the crime and link the tool(s) to the criminal. Investigators compare marks by examining detailed photos or silicone casts of the marks and collect trace evidence (such as residue) left behind by the tool. 

There are three types of tool marks:

  • Moulded: The object is inserted into the surface.
  • Slipped: The object is dragged across the surface.
  • Combo: The object is both inserted and dragged across the surface.

Premise: Tool Marks at the Point of Entry
Police survey the home and locate the point of entry at the back of the house. They find that the backdoor leading into the kitchen has clearly been vandalized. Pronounced tool marks are visible around the doorframe and the doorknob. They take photos and dust the door for fingerprints. While no prints are uncovered, the tool marks left on the door can be analyzed to identify the means used to enter the home.

In this activity, the student detectives’ task is to explore the types of marks made by a variety of tools and compare the marks on the Grizzly family’s back door.

Objectives

  • Carefully compare, analyze and record tool mark evidence to infer a likely suspect.

Materials

  • Per Student:
    1 Crime Fighter’s Case Book
    pencil

  • Per Station:
    9 large cubes of modelling clay
    three tools, labelled A, B, and C (must include one hammer)
    Photo of tool mark evidence

Key Questions

  • What is the difference between the types of marks made by each tool?
  • What is the difference between the types of marks made by the same tool when used in different ways?
  • What are the similarities and differences between the marks you’ve made with the different tools, and the marks you see in the photograph?
  • Do you think that the tool marks differ with the type of material (e.g., door, window, cushion etc.) the tool interacts with?

What To Do

Preparation

  1. For each tool, provide three large cubes of modelling clay.
  2. Provide a clear copy of the photo of tool mark evidence for student detectives to examine.

Activity

  1. Students create samples of tool marks for each of the three tools:
  • For a moulded mark type, students should insert the tool into the clay and pull it out.
  • For a slipped mark type, students should draw the tool across the surface of the clay.
  • ​For a combo mark type, students should insert the tool, then draw it across the clay.
  1. Detectives then carefully compare the tool marks shown in the photo to the tool marks they’ve made on the cubes on modelling clay and decide which tool caused the damage to the Grizzlys’ back door.