Forensic Science Exam 4

explosive

a substance or device that contains high amounts of stored energy

energy is released rapidly through a chemical reaction, release of pressure, or nuclear reaction

categorized as low or high based on whether or not the blast velocity exceeds the speed of sound

low explosives

blast velocity does not exceed the speed of sound

ex: black powder and smokeless powder

black powder

mixture of carbon, sulfur, and potassium nitrate

is a low explosive

smokeless powder

mixtures of nitroglycerine, nitrocellulose and various inert ingredients to improve stability

is a low explosive

nitroglycerine

a highly sensitive shock-detonated liquid

trinitrotoluene (TNT)

fairly stable yellow crystals with a blasting cap

commonly used in mining

ammonium nitrate fuel oil (ANFO)

mix of fertilizer and diesel fuel detonated with a blasting cap

used in the OKC bombing

crude explosives

explosive chemicals contained in a section of sealed pipe, can, or bottle with a wick protruding

ex: pipe bombs, aerosol can, and bottle bombs, pressure cooker bomb

easy-to-make bombs made from readily available materials

what to look for at the scene of a bombing

shreds of the container spread quite far

embedded shards in other objects

fragments of tissue and bone

may have to look pretty far from site

take scraping of all burn marks, chemical residue, and scorched materials to analyze for nitrates or other residual compounds

gun types

most are civilian and for personal use

handguns

rifles

shotguns

many have interchangeable ammunition

types of handguns

semi-automatic pistols

single-action revolvers

double-action revolvers

semi-automatic pistols

detachable magazine in the handle

internal or external spring loaded

trigger launches firing pin into primer→ powder→ bullet

fire as fast as you can pull the trigger

single-action revolvers

hammer must be locked back before shooting

bullets dropped into rotating cylinder, hammer released, trigger pulled

old-school cowboy guns—have to lock the hammer

double-action revolvers

can be cocked first or fired simply by repeatedly pulling the trigger

don’t have to cock the hammer each time

caliber

bullet diameter

common handgun calibers

.22 Long rifle and .22 magnum

.38 special

9 mm Luger (aka 9×19 mm or 9mm NATO)

.357 magnum

.40 S&W

.44 magnum

.45 auto

.45 Colt

.22 long rifle and .22 magnum

magnum is just a longer shell with more powder

versatile (can be used in rifles and handguns)

.38 special

is actually just a .357”

9 mm Luger (aka 9×19 mm or 9 mm NATO)

semi-automatic

doesn’t have a lip like revolver rounds

no lip so they can be stacked in a magazine

.357 magnum

military designation

original revolver round

elongated case of a .38 special and a different kind of bullet

.45 Colt

old-west single action revolver round

gun barrel markings

produced from a solid bar of steel that has been hollowed out by drilling (aren’t cast)

microscopic drill marks left on the inner surface make each unique—often leaves a unique impression on a bullet

types of rifles

can be pump, lever action, or bolt action

civilian models are single-shot or semi-auto

calibers range from .22- >.500

common rifle calibers

.22 long rifle and .22 magnum

.223 Remington (aka 5.56×45 mm or M855)

.243 Winchester

.308 Winchester

.30-06 Springfield (aka M2)

.30-30 Winchester

.45-70 Government

.243 Winchester

small caliber bullet, large powder charge

“rifled”

describes the barrels of handguns, rifles, and some shotguns

inner surface of the barrel leaves its markings on a bullet passing through it—increases accuracy and puts a spin on the bullet so it won’t deviate from its trajectory

shotguns

ammunition consists of a plastic shell which contains many led or steel pellets of various sizes or a solid lead slug

size is based on gauge (smaller gauge=bigger gun)— 10 ga> 12 ga

.410 is a caliber, not a gauge

gun barrel markings

gun barrel is produced from a solid bar of steel that has been hollowed out by drilling

microscopic drill marks left on barrel’s inner surface make each barrel unique

are “rifled” to increase accuracy and put a spin on the bullet so it won’t deviate from its trajectory. also leaves marks on bullets passing through

grooves

parts of barrel cut out in rifling (lower surfaces)

impart a rapid spin on the bullet to ensure accuracy

lands

original bore remaining between the grooves

the original barrel

barrel caliber

diameter of the gun barrel measured between opposite lands

rifling pattern

specific to a manufacturer in terms of degree and direction of twist

can determine who made a gun based on the patterns—manufacturers keep their tools so they can be matched if needed

striations

fine lines found in the interior of the barrel from minute imperfections found on the rifling cutter

like a fingerprint for the barrel

cartridge case comparison

shape of firing pin impressed into the primer on the _________

impressed with the surface markings of the breechblock

center fire

primer in the middle, little dimple in case where primer would be

rime fire

no actual primer, whole back of case is the primer

other distinctive markings on the shell are a result of

ejector, extractor, magazine

gunpowder residue

when a firearm is discharged, unburned, and partially burned particles of gunpowder and primer chemicals are propelled out of the barrel and back toward the shooter

distribution of _____ particles and other discharge residues around a bullet hole permits an assessment of the distance from which a handgun or rifle was fired

close range shot

less than one inch from the target a star-shaped stellate tear pattern around the bullet hole forms

12-18 inches

halo of vaporous lead smoke deposited around a bullet hole

up to 36 inches

presence of spattered specks of unburned powder grains

bullet wipe

usually doesn’t deposit any powder residues and only indication is a dark ring around the hole at distances of more than three feet

primer residue on hands

barium and antimony (from the primers) can be found on the relevant portions of a suspect’s hands

serial numbers

has to be etched into metal, even on plastic guns

often etched multiple places

can be restored through chemical etching

chemical etching

acid used to wear down soft scratched off metal and leave behind the harder, dense metal underneath. the metal in the stamped zone is placed under a permanent strain that extends a short distance beneath the original numbers

factors to consider for a bloodstain when determining direction, drop distance, and impact angle of a bloodstain

surface texture, stain shape, size, and location

direction of travel

pointed end of a bloodstain always faces its direction of travel

unless it’s blood that has trailed down an angled surface

impact angle of blood on a flat surface

determined by measuring the degree of circular distortion

at right angles the blood drop is circular, as the angle decreases the stain becomes elongated

finding the origin of a blood spatter

can be found by drawing straight lines through the long axis of individual bloodstains

point of convergence represents the origin point

shooting wound

may leave a forward spatter from an exit wound and back spatter from an entrance wound

arterial spatter

results from an injury to a main artery or the heart

large spurted stain pattern for each time the heart pumps

expirated blood pattern

pattern created by blood that is expelled from the mouth or nose from an internal injury

transfer/contact pattern

an object with blood on it touches one that does not have blood on it

skeletonization

edges of a pool of blood will dry to the surface

trail pattern

a series of drops that are separate from other patterns, formed by blood dripping off an object or injury

minutae

ridge characteristics

as many as 150 on the average finger

latent/invisible fingerprints

prints deposited on a surface that are invisible to the eye

print transfer

when a finger touches a surface, perspiration and oils are transferred onto that surface, leaving the finger’s ridge pattern

three classes of prints

loop

arch

whorl

ulnar loop

loop opens toward the little finger

radial loop

loop opens toward the thumb

arch types

plain or tented

visible prints

made when fingers tough a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink

plastic prints

ridge impressions left on a soft material such as putty, wax, soap, or dust

carbon powders

can be applied with a brush or magnetic wand and adhere to body oils of the print

prints on porous surfaces

generally require treatment with a chemical

iodine fuming

heating iodine crystals that cause vapors which combine latent prints to make them visible

super glue fuming

develops latent prints on nonporous surfaces such as metals, electrical tape, leather, and plastic bags

transporting

lifting with adhesive tape

tape placed on a card that provides a good background contrast with the powder

hair anatomy

extends from a root or bulb embedded in the follicle, continues into a shaft, and terminates at the tip end

shaft

cuticle, cortex, and medulla

subjected to the most intense examination by the forensic scientist

cuticle

scale structure covering the exterior of the hair

scales always point toward the tip of the hair

scale pattern is useful in species identification

cortex

main body of the hair shaft

embedded with pigment granules that impart hair with color

color, shape, and distribution of granules provide important point of comparison

medulla

cellular column running through the center of the hair

medullary index

measures the diameter of the medulla relative to the diameter of the hair shaft

may or may not be present even in different hairs of the same individual

have different shapes depending on the species

follicular tag

translucent tissue surrounding the hair’s shaft near the root

can be individualized using DNA analysis

comparing hairs

color, length, and diameter

scale structure, medullary index, and medullary shape are important in animal hair identification

important features for comparing human hair

presence or absence of a medulla

distribution, shape, and color intensity of the pigment granules in the cortex

anagen (early growth)

most likely to detect DNA in hair roots

catagen (middle growth phase)

less likely to detect DNA in hair roots

telogen (final growth phase)

least likely to detect DNA in hair roots