forensics midterm firearms


positive impression


can be 2D or 3D deposition of a substance onto a substrate


negative impression


removal of a substance from the receiving surface e.g. powder or dust


shoe print class characteristcs


size and brand


individual characteristics of shoes


unique wear patterns, cuts, foreign objects inbeded in tread


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)


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


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


Amido Black-turns black blue
Leucocrystal violet _turns purple water based and sprayed on


chemical enhancement used for impession in blood


firearms (class characteristics)


bullet, caliber, general rifling, casing, caliber, brand, shape of firing pin mark


individual characteristics ( fire arms)


bullets, minute random/marking/straitions, casings, impressed marks/striated marks, due to structural irregularites/ variations


handguns
long guns


types of firearms


single shot-no casing
revolvers -no casing
semiautomatic leaves casing


types of handguns 3


rifles
shotguns


types of long guns


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


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


rifling


spiral grooves that impart spin to the projectile when it is fired (so the bullet will go straight)


no , smooth bore


does a shot gun have rifling?


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


impressed marks on casing


breechblock firing pin extractor ejector


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


particles


strippling, tattooing


smoke


soot, fouling


distance determination


gun powder residue permits...the asessement of the distance from which a weapon was fired


contact to <1'


smoke like vaporous lead surrounds entrance hole: fibers scorched stelle shape hole


12-18"


halo of vaporous smoke, specks of unburned or partially burned powder grains observed up to 25"


over 3'


no powder residue or powder grains bullet wipe around entrance hole


lead, barium, and antimony


all 3 of these must be present in primer residue


tool marks


any impression cut, gouge, or abrasion caused by a tool coming into contact with another object


class ( toolmarks )


size shape of mark


individual tool marks


random nicks and breaks through use or random striations from manufacturing process


bitemarks


swab for DNA photograph cast