when tool is pressed into soft material Show outline of tool Sliding when tool is slides across the surface Has a pattern of parallel striations Class characteristics are hard to determine because many tools make similar sliding marks ID: 1003159
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1. Types of Tool MarksCompression: when tool is pressed into soft materialShow outline of toolSliding: when tool is slides across the surfaceHas a pattern of parallel striationsClass characteristics are hard to determine because many tools make similar sliding marks Cutting: combination of compression and sliding 1Quality of the tool mark is affected by receiving surface:--Good recipients =Soft metals, plastics, and painted surfaces --Bad recipients= Raw wood and hard metal
2. Identify/search for mark:First places to check: points of entry, locks, safes, etc.Do not to alter existing tool marks—no attempt to fit tool into markDocumentNotes, sketch, Photographs—show location, but not useful in lab comparisonCollect: Take the item back to the lab if possibleA cast of the tool mark should be made if the object cannot be transportedSilicone rubber is the ideal casting materialProcessing of tool marks at crime scene2
3. Laboratory Examinations of Tool MarksTest marks for Microscopical ComparisonsMake a test mark on a receiving surface to replicate the mark at the scene, using ductile or malleable material (to avoid damage) and the same toolCompare the test and questioned marksExamining Individual CharacteristicsResult from manufacturing processes, wear, and damage from misuse3
4. Laboratory Examinations of Tool Marks: Conclusions that can be made Positive ID Class characteristics and individual characteristics match Negative ID Class characteristics do not match Inconclusive Class characteristics match but that insufficient match in individual characteristics 4
5. Hammer marks on the heads of nails and bradsExtrusion marks on pipeMachining marks on metal shavingsExtrusion marks in plastic film, plastic cling wrap, and plastic bagReam marks on sheets of flat glassPunch defect marks on illicitly manufactured drug tabletsTool Marks onManufactured Items5
6. Striation Matching for Personal IdentificationHuman finger and toe nails have striation patterns on their upper and lower surfaces.Size and spacing of striations is determined by dermal ridges in nail bedNails are prepared for examination by pressing them between two flat surfacesSilicone rubber casts of nail ridges can be made and compared microscopically 6