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John H. Dillon, Jr. “Module 13: Toolmark Identification.” Firearm Examiner…
John H. Dillon, Jr. “Module 13: Toolmark Identification.” Firearm Examiner Training, National Forensic Science Technology Center, projects.nfstc.org/firearms/module13/fir_m13.htm.
Tool Manufacture
Metal Forming Techniques: cold forging, upset forging, drop forging, casting, blanking, shearing, stamping, drawing, swaging, and extrusion
Modern Machining Techniques: electrical discharge machining, laser machining, electrochemical machining, etching, hydrodynamic machining, ultrasonic machining, electron beam machining
Cutting Operations
Milling
Face milling, peripheral milling, and end milling
Conventional milling and climb milling
Other Cutting Operations: shaping, planing, drilling, reaming, broaching, sawing, filing, and abrasive machining
Lathe Operations: turning, facing, and boring
Toolmark Examination
Comparison of Evidence Toolmarks and Test Marks: make sure to document area of best agreement
Inconclusive Results: can be caused by the fact that they aren't actually a match, damage to original toolmark, damaged tool that made the mark, or too many subclass characteristics
Production of Test Toolmarks: must be done a number of times to get a comparable mark
Intercomparison: compare toolmarks from different crimes in order to link them
Microscopic Comparisons: microscopes calibrated, appropriate level of magnification, keep same lighting across comparisons
Intercomparison of Fractured Objects
Microscopic Procedures: administrative requirements, presence of trace evidence, necessity of latent fingerprint examinations, clean toolmarked area
Reverse Lighting Technique: used to show that fractured objects were once whole
Basic Toolmark Identification
Pattern Identification: mental process of determining whether the striated marks on two objects correspond
Consecutive Matching Striae: a way to quantify whether two patterns match or not
Physical Characteristics: class, subclass, and individual characteristics
AFTE Theory of Identification: three principles
Tool Actions: scraping, pinching, shearing, slicing, prying, gripping, crimping
Sufficient Agreement and Best Known Nonmatch: usually two examiners examine the patterns in order to achieve this
Reloading and Handloading: cause different marks than normal firing- holding, resizing toolmarks
AFTE Range of Conclusions: identification, inconclusive, elimination, unsuitable
Incidental Toolmarks
Striated toolmarks: tool moves parallel to another object
Impressed toolmarks
Equipment
Stereomicroscope
Microscope lighting options
Comparison Microscope
Imaging Equipment