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Firearms Examiner Training

Module 13: Toolmark Identification

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illustration of a gun being fired
National Institute of Justice (NIJ) (see reuse policy).


Author: John H. Dillon, Jr.
Headshot of Author John H. Dillon, Jr
National Institute of Justice (NIJ) (see reuse policy).
Jack Dillon earned a B. S. from the United States Naval Academy and an M. Ed. from the University of Virginia. Commissioned in the United States Marine Corps in 1964, he attained the rank of Captain of Marines. Appointed a Special Agent, FBI, in 1970, he investigated diverse criminal violations, including organized crime, bank robberies, extortions, and kidnappings. In 1976 he received orders to the Firearms/Toolmarks Unit of the FBI Laboratory for training as an examiner, where he evaluated evidence and provided on-site field support in domestic cases, as well as abroad. He also designed and taught basic and management-level forensic courses at the FBI Academy, Quantico, Virginia, 1982-1988. Jack retired from the FBI as Chief of the Firearms/Toolmarks Unit in 1994, and continues to consult in forensic firearm cases and in training design and delivery.



Toolmark examinations and comparisons represent the core area of study for firearm and toolmark examiners. The conceptual and practical aspects of toolmark identification provide the skills necessary for firearms identification; firearm identification is a specialized subset of toolmark identification. There are potentially many more variables in terms of the marks to be examined.

As a forensic discipline, microscopic comparison and potential identification of striated or impressed toolmarks as having been made by the same tool are central to the identification of toolmarks.

The foundation for this technique is based on the following concepts:

  • A tool is defined as the harder of two objects which, when brought into contact with each other, results in the softer object receiving a toolmark.
  • Tools (e.g., screwdrivers, firearms, bolt cutters, etc.) will bear unique microscopic characteristics due to the manufacturing processes they undergo and use and abuse.
  • These characteristics will mark surfaces (e.g., locks, cut wires, fired bullets, etc.) with class and individual characteristics.
  • These class and individual characteristics are reproducible and identifiable with a particular tool.


At the conclusion of this module the student should be able to do the following:

  • Identify the common metal shaping operations used in the manufacture of tools, including
    • common cutting operations based on the formation of metal chips,
    • common metal forming operations not involving cutting,
    • modern metal machining techniques.
  • Describe the following concepts as they relate to the formulation of conclusions relating to toolmark examination and comparison:
    • Class characteristics
    • Individual characteristics
    • Subclass characteristics
    • AFTE Theory of Identification
    • Pattern matching
    • Sufficient agreement
    • Best known nonmatch
    • Consecutive matching striae (CMS)
    • AFTE Range of Conclusions
  • Explain the differences between the terms
    • identification,
    • inconclusive,
    • elimination,
    • unsuitable.
  • Itemize the essential items of equipment necessary to carry out the comparison microscopy of toolmarks.
  • Summarize the prerequisites that must be addressed prior to initiating any examination or comparison of toolmarked evidence.
  • Describe the examination protocol for the microscopic comparison of the class and individual characteristics represented by toolmarks.
  • Describe the examination protocol for the examination and comparison of fracture marks.

AFTE Knowledge and Ability Factors

14. Knowledge of how to properly document evidence and analytical results (through notes, sketches, photography, reports, etc.)
15. Knowledge of the techniques and procedures used to properly mark evidence (when appropriate)
26. Knowledge of definitions of class, subclass, and individual characteristics and the differences between them
27. Knowledge of the sources of class, subclass, and individual characteristics
38. Knowledge of how and when to use various vises, clamps, and restraining devices
114. Knowledge of proper use of tools and materials for test marks
116. Knowledge of the interactive nature of the tool/toolmark process and the transference of class, subclass, and individual characteristics
117. Knowledge of impressed (static) vs. striated (dynamic) toolmarks
118. Knowledge of the best agreement possible in situations of known nonmatches when comparing toolmarks
119. Knowledge of the principles of preparing test marks and the effects of test materials in the production of testfired cartridge components and toolmarks for comparison
4. Ability to select the appropriate casting materials (casting of bullets/toolmarks)
17. Ability to select proper casting material and technique (mentioned above)
19. Ability to understand and interpret technical data output from laboratory instruments
21. Ability to recognize discrepancies or inconsistencies in analytical findings and determine their cause and significance
23. Ability to recognize the limitations of tests and interpretations
41. Ability to identify reloaded ammunition as having been assembled by the same equipment by determining that specific reloading tool(s) came in contact with cartridge components
48. Ability to recognize and properly align reproducible striae arrays sufficient for identification purposes
49. Ability to recognize, determine the source of, and differentiate between class, subclass, and individual characteristics on bullets, cartridges, cartridge cases, and in nonfirearm-related toolmarks
53. Ability to distinguish between the quality and quantity of matching striae in a true identity and that observed in known nonmatches
57. Ability to recognize any manufacturer-induced characteristics
71. Ability to make determinations in toolmark comparisons (both firearm and nonfirearm toolmarks) regarding: identifications, exclusions, and inconclusives
72. Ability to recognize patterns (profiles, etc.) produced by various tool-working surfaces

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