Toolmark SC

Toolmarks

  • Toolmarks are significant in forensic science as evidence at crime scenes.

What Are Toolmarks?

  • Toolmarks are impressions, cuts, scratches, gouges, or abrasions left when a tool contacts a softer object.

  • Example: Using a screwdriver to pry open a locked window creates toolmarks on the window.

Types of Tools

  • Tools can be classified by design:

    • Locking pliers

    • Needle nose pliers

    • Slip joint pliers

    • Tongue and groove pliers

    • Lineman's pliers

    • Diagonal cutters

    • Wire cutters/strippers

    • Pipe wrenches

    • Circular cutting tools

    • Chisels

    • Screwdrivers

    • Pry bars

    • Bolt cutters

    • Hammers

Tool Action Classification

  • Tools can also be classified by their action, which affects the marks left behind:

    • Compression Tools: Designed to compress (e.g., hammers, chisels).

    • Flat Action Tools: Work parallel to the surface (e.g., screwdrivers, pry bars).

    • Gripping Tools: Use opposing jaws to hold (e.g., vise grips).

    • Pinching Tools: Designed to cut using a pinching action (e.g., bolt cutters).

    • Shearing Tools: Use two blades on adjacent planes (e.g., scissors, tin snips).

Importance in Criminal Investigations

  • Toolmarks are commonly found at burglary scenes with forced entry, especially on door frames and windows.

  • Investigators look for suspects' toolboxes, as tools leave unique scratch marks used to match them to crime scene evidence.

Examination of Toolmarks

  • Toolmarks can reveal class characteristics such as size and shape, but rarely individual characteristics.

  • Individual characteristics appear as unique nicks and breaks on the tool surface due to wear.

Microscopic Irregularities

  • Tools exhibit random striations and microscopic irregularities during manufacturing and usage.

  • These imperfections reflect the unique nature of tools, making it unlikely for identical patterns to exist on two different tools.

Striations and Toolmark Comparisons

  • If a tool scrapes against a softer surface, it leaves a series of striated marks.

  • In the crime lab, castings of toolmarks are made, allowing comparisons through a microscope.

  • Positive comparisons occur when sufficient striations match between evidence and test markings.

Collection and Preservation of Toolmarks

  • The entire object with a toolmark should be collected when possible. If not, photographs and casts are alternatives.

  • Common casting materials include liquid silicone or dental plaster. Caution must be taken not to alter the original mark.

Types of Toolmarks

  • Impressed Toolmarks: Produced by applying pressure to a tool against an object, creating a mirror image of the tool’s surface.

    • Commonly caused by tools like bolt cutters.

  • Striated Toolmarks: Created when a tool moves across another object, leaving friction/scratch marks.

    • Screwdrivers are commonly involved in such instances.

Conclusion

  • Toolmarks provide critical evidence for forensic investigations, enabling the association of tools with crimes based on unique markings.