forensics midterm firearms

  1. positive impression
    can be 2D or 3D deposition of a substance onto a substrate
  2. negative impression
    removal of a substance from the receiving surface e.g. powder or dust
  3. shoe print class characteristcs
    size and brand
  4. individual characteristics of shoes
    unique wear patterns, cuts, foreign objects inbeded in tread
  5. collection of footprints
    • photography
    • casting (for 3D impression)
    • gelatin lifer ( 2-D impression)
    • electrostatic dust lifter -uses static 2Dd impressions
    • collect item with print impression (shirt)
  6. Photography of shoe print
    • use tripod
    • make sure camera lens is perendicular to the impression
    • take shot without scale then with a scale and identifier
    • make sure impression fills entire frame
    • use OBLIQUE lighting with flashlight or flash
    • lighting less then 45% to print
    • 4 different shots even in daylight
  7. obtaining known standards (tire impressions and shoes)
    • finger print ink method -Rolled on paper
    • vaseline method -vaseline on tred and rolled on paper process with black fingerprint powder
    • specific to shoes
    • collect
    • biofoam
  8. Amido Black-turns black blue
    Leucocrystal violet _turns purple water based and sprayed on
    chemical enhancement used for impession in blood
  9. firearms (class characteristics)
    bullet, caliber, general rifling, casing, caliber, brand, shape of firing pin mark
  10. individual characteristics ( fire arms)
    bullets, minute random/marking/straitions, casings, impressed marks/striated marks, due to structural irregularites/ variations
  11. handguns
    long guns
    types of firearms
  12. single shot-no casing
    revolvers -no casing
    semiautomatic leaves casing
    types of handguns 3
  13. rifles
    types of long guns
  14. caliber
    the diameter of the bore of a rifled firearm expressed in hundreds of an inch or mm .22 caliber, 9mm, .30 caliber, 7.62mm, .357 caliber
  15. gun barrel
    hollowed out by drilling during manufactoring cause microscopic drill marks that are random and irregular also impressed the inner surface with spiral grooves
  16. rifling
    spiral grooves that impart spin to the projectile when it is fired (so the bullet will go straight)
  17. no , smooth bore
    does a shot gun have rifling?
  18. striations in the barrel caused by
    minute imprerfections on the rifling culters surface minute chips of steel pushed through random distribution and irregularites are impossible to duplicate to any two barrels even when manufactured in succession
  19. impressed marks on casing
    • breechblock
    • firing pin
    • extractor
    • ejector
  20. gunpowder residues
    • ammunition is propelled by the expanding gases created by ignition of smokeless powder of nitrcellube in cartridge
    • unburned and partically burned particles of gunpowder plus smoke are propelled out
  21. particles
    strippling, tattooing
  22. smoke
    soot, fouling
  23. distance determination
    gun powder residue permits...the asessement of the distance from which a weapon was fired
  24. contact to <1'
    smoke like vaporous lead surrounds entrance hole: fibers scorched stelle shape hole
  25. 12-18"
    halo of vaporous smoke, specks of unburned or partially burned powder grains observed up to 25"
  26. over 3'
    no powder residue or powder grains bullet wipe around entrance hole
  27. lead, barium, and antimony
    all 3 of these must be present in primer residue
  28. tool marks
    any impression cut, gouge, or abrasion caused by a tool coming into contact with another object
  29. class ( toolmarks )
    size shape of mark
  30. individual tool marks
    random nicks and breaks through use or random striations from manufacturing process
  31. bitemarks
    • swab for DNA
    • photograph
    • cast
Card Set
forensics midterm firearms