Chapter 8 Forensic Science

2 principal differences between rifled firearms and shotguns

1) ammunition; 2) barrel

electrostatic

2- dimensional imprints at a crime scene can be lifted using an _______________ lifting device.

tool mark

A _______ _________ is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object.

infrared

A __________ photograph may help visualize gunpowder deposits around a target.

single

A cartridge case can be individualized to a ___________ weapon.

odontologist

A forensic __________________ might be asked to analyze bite marks on a person or object found at a crime scene. If a sufficient number of points of similarity exist between the test and suspect marks, the forensic _______________ may conclude that the marks were made by one particular individual.

smooth

A shotgun has a _________________ barrel without the lands and grooves found in a rifle.

comparison

A sufficient number of points of ______________ or the uniqueness of bloody shoe prints will show that both the questioned and test impressions originated from one and only one source.

portable electrostatic

An imprint may be lifted using lifting sheets or a ___________ _____________ lifting device.

yard

As a rule of thumb, the spread in the pattern made by a 12-gauge shotgun increases 1 inch for every _________ of distance from the target.

gunpowder; primer

Current methods for identifying a shooter rely on the detection of ____________ and ______________ residues on the hands.

nitric

Firings with all types of ammunition can be detected by hand swabbings with ________ acid.

chemical enhancement

In areas where a bloody footwear impression is very faint or where the subject has tracked through blood, leaving a trail of bloody impressions, _____________ ________________ can visualize latent or nearly invisible blood impressions.

scanning electron

Microscopic primer and gunpowder particles on the adhesives applied to a suspected shooter's hand can be found with a _____________ _____________ microscope.

barrels

No 2 rifled ____________ have identical striation markings.

identical; coincide

Not only must the lands and grooves of the test and evidence bullet have _______________ widths, but the longitudinal striations on each must also __________________.

photography; casting

Shoe and tire marks impressed into soft earth at a crime scene are best preserved by ________________ and ______________.

shell

Shotgun ammunition, called a _________, contains numerous ball-shaped projectiles, called shot.

hand; long

The 2 categories of firearms are _________guns and ________guns.

broach cutter

The _________ _________ process of rifling consists of a series of concentric steel rings, with each ring slightly larger than the preceding one. as the _________ ____________ passes through the barrel, it simultaneously cuts all grooves into the barrel at the required depth. It rotates as it passes through the barrel giving the grooves their desired direction and rate of twist.

FBI

The _________ maintains a record known as the General Rifling Characteristics File, which contains a listing of class characteristics, such as land and groove width dimensions, for known weapons.

mandrel

The ___________ rifling or hummer forging process involves no cutting of metal. A __________ or rod of hardened steel is machined so its form is the reverse impression of the rifling it is intended to produce. It is inserted into a slightly oversized bore, and the barrel is compressed with hammering or heavy rollers into the form of the ____________.

button process

The _____________ ___________ of rifling involves no cuttings. A steel plug impressed with the desired number of grooves is forced under extremely high pressures through the barrel. A single pass of the plug down the barrel compresses the metal to create lands and grooves on the barrel walls that are negative forms of those on the steel plug. The plug rotates to produce the desired direction and rate of twist.

microscopic

The _______________ drill marks left on the barrel's inner surface are randomly irregular and in themselves impart a uniqueness to each barrel.

breechface

The __________________ is the rear part of a firearm barrel.

NIBIN

The automated firearms search system developed by the FBI and ATF as a unified system incorporating both DRUGFIRE and IBIS technologies available in prior years is known as _______________.

stellate

The blowback of muzzle gases may produce a ___________ (star-shaped) tear pattern around the hole.

powder residues

The clothing of the victim of the shooting must be handled so as to prevent disruption of ____________ _____________ around bullet holes.

how criminalists restore obliterated serial numbers on weapons

The criminalist applies a suitable etching agent to the area that has been defaced. The metal in this area dissolves at a faster rate than the unaltered metal surrounding it, thus permitting the etched pattern to appear in the form of the original numbers.

chocolate

The dermal nitrate test has fallen into disfavor because of its lack of specificity. _________________ does not give a misleading positive reaction to this test.

distance

The distribution of gunpowder particles and other discharge residues around a bullet hole is directly related to the _____________ from which the gun was fired.

ridges, valleys

The edges of any tool display a series of microscopic irregularities having the appearance of ____________ and _____________. These marks are created during the machining processes used to cut and finish the tool, or from nicks and breaks that occur during normal use of the tool.

signature

The firing pin, breechblock, and ejector and extractor mechanism, the magazine, the clip, and the fire chamber walls also offer a highly distinctive ____________ for individualism of cartridge cases as they leave distinctive markings on the shell casing.

twist

The number of lands and grooves and their direction of ___________ are obvious points of comparison during the initial stages of an examination.

lands

The original part of the bore left after rifling grooves are formed are called the ___________.

25

The presence of scattered specks of unburned and partially burned powder grains without any accompanying soot can often be observed at distances up to ______ inches.

damage; wear

The shape and pattern of imperfections on tools are further modified by __________ and ________ during the life of the tool.

powder-residue

To determine the precise distance from which a gun has been fired requires a comparison of the __________-___________ pattern on the victim's clothing or skin against the patterns made from test-firing the suspect weapon.

striations

To make a match between a test bullet and a recovered bullet, the lands and grooves of the test and evidence bullet must have identical widths, and the longitudinal _______________ on each must coincide.

number

Tool marks compare only when a sufficient ___________of striations match between the evidence and test markings.

long guns

_________ _________ are either rifles or shotguns.

Colts

__________ are not manufactured with class characteristics.

nitrites

__________ are one type of chemical product that results from the incomplete combustion of smokeless (nitrocellulose) powder.

Marlin

___________ rifles produce bullets with rifling marks that set them apart from most other manufactured weapons, due to process they use called microgrooving.

factors that determine the spread of a shotgun blast

barrel length, size and quantity of pellets fired, quantity of powder charge used to propel the pellets, and the choke of the gun

advantage of SEM

its enhanced specificity over swabbing

primary concern of the field investigator when recovering bullets and cartridge cases

protection of class and individual markings

base; nose

Recovered bullets are initialed on either the ____________ or ___________ of the bullet.

5 factors that influence the amount of gunpowder residue deposited on a target

1) barrel length; 2) caliber; 3) type of ammunition; 4) type of weapon; 5) condition of weapon

3 characteristics of a gun barrel

1) caliber; 2) the number of lands and grooves; 3) the direction of twist of the lands and grooves.

3 most common types of handguns

1) single-shot handguns; 2) revolvers; 3) semi-automatics

2 reasons why striations on bullets fired from the same gun may vary slightly

1) the presence of dirt or grit; 2) striation markings on a barrel are not permanent structures. They are subject to continuing change and alteration through wear as succeeding bullets traverse the length of the barrel.

12 - 18

A halo of vaporous lead (smoke) deposited around a bullet hole normally indicates a discharge ______ - ______ inches from the target.

determination

A trained firearms examiner makes the final ________________ whether or not 2 bullets were fired by the same gun.

individual

A wear pattern, cut, gouge, or other damage pattern can impart ________________ characteristics to a shoe.

single; double

All handguns can be classified as _________ action or __________ action.

pencil

An investigator would not pick up a weapon by its barrel with a __________ or stick in order to protect fingerprints because this may disturb powder deposits, rust, or dirt lodged in the barrel, and consequently may alter the striation markings on test-fired bullets.

low

Analysis of primer residue from a suspect's hands produces a _______ rate of positive results because primer residues remains on hands only for a short time and are easily removed by rubbing or washing.

.22

Analysis of primer residues cannot be used to detect firings with most ______ caliber rim-fire ammunition because the primer for this ammunition often does not contain characteristic elements associated with primer residues.

characteristics

Any differences in the __________________ imparted by the lands, grooves, and their direction of twist eliminates the possibility that both bullets traveled through the same barrel.

intact

Because minute traces of evidence such as paint and fibers might be adhering to a recovered bullet, the investigator must take care to leave these trace materials ___________.

why a firearms examiner test-fires bullets from a suspect barrel

Because there is no other practical way to directly compare the markings on the fired bullet and those found within a barrel.

photographed

Before any impression is moved or otherwise handled, it must be ________________ to show all the observable details of the impression. This is merely a backup procedure in case the impression is damaged before reaching the crime lab. It is preferable for the examiner to receive the actual impression for comparison to the suspect object that made the impression.

shape; density

By comparing residue patterns from the test firings to those found at the crime scene, the examiner may find enough similarity in _________ and ____________ on which to base an opinion as to the distance from which the shot was fired.

greater

Chokes are sometimes found on shotguns where they function to constrict the end of the barrel. The speed and distance traveled by pellets fired from a narrow choke is __________ than the speed and distance traveled by pellets fired from a shotgun with a wide choke.

barium; antimony

Determining whether an individual has fired a weapon is done by measuring the elements ______________ and ____________ present on the hands.

striation markings

Discharged evidence bullets must be carefully handled to avoid damage to the ____________ _______________ that are left on a bullet as it passes through the barrel.

suicide

Distance determination can also determine whether a shooting was a _____________, which usually involves a very close-range gunshot wound.

spread

Distance determination for a shotgun blast is made by measuring the ___________ of the discharged shot. The wider the __________, the farther the shooter was from the target.

SEM; infrared

Gunpowder residue patterns can be detected by ________ and _____________ photography (Geiss Test).

bullet wipe

If a firearm has been fired more than 3 feet from a target, usually no residue is deposited but a dark ring , known as ___________ _________, is observed.

self-defense

If a suspect pleads _______-_________ as the motive for a shooting, determining how far apart the suspect and victim were at the time of the shooting can establish the facts of the incident.

trigger guard

If the recovery of latent prints is a primary concern, it is best to hold the weapon by the edge of the ____________ __________ or by the checkered portion of the grip.

1 inch

If the weapon is fired less than ___ _______ from the target, a heavy concentration of smoke-like vaporous lead usually surrounds the bullet entrance hole.

cast

Objects bearing tool marks should be submitted intact to the crime lab or a __________ should be taken of the tool mark.

contact

Often, loose fibers surrounding a ___________ hole show scorch marks from the flame discharge of the weapon, and some synthetic fibers show signs of being melted as a result of the heat from the discharge.

thumb web; back

Primer residues are typically found on the __________ ______ and the _______ of the firing hand of the shooter, because these areas are in closest proximity to gases escaping along the side or back of the gun during discharge.

strain

Restoration of serial numbers is possible because in the stamped zone the metal is placed under a permanent __________ that extends beneath the original numbers.

cannot

Shotgun pellets ___________ be individualized to a single weapon.

irregularities

Structural variations and ________________ caused by scratches, nicks, breaks, and wear permit the criminalist to relate a bullet to a gun, a scratch or abrasion mark to a single tool, or a tire track to a particular automobile.

brand name

The ________ ________ of a tool is the least likely factor to be considered by the examining tool mark technician.

Greiss

The ________ test is a method for locating powder residue involves transferring particles embedded on the target surface to chemically treated gelatin-coated photographic paper. It can reveal whether powder residues from a gunshot are present and can also help determine the distance from the shooter to the target.

gauge

The _________ of a shotgun is directly related to the diameter of its barrel.

hook cutter

The __________ _____________ method of rifling a barrel is no longer used.

revolver

The ___________ features several firing chambers located within a revolving cylinder.

disadvantage

The ______________ of making a silicone cast of a tool mark impression is that, even under the best conditions, the clarity of many of the tool mark's minute details will be lost or obscured in a photograph or cast.

individual

The ___________________ characteristics of a rifled barrel are formed by striations impressed into the barrel's surface.

foul play

The absence of characteristics consistent with a close-range shot in suspected suicide cases is a strong indication that the wound was not self-inflicted and signals the possibility of _________ _________.

analogous

The advent of computerized imaging technology has made possible the storage of bullet and cartridge surface characteristics in a manner ____________ to automated fingerprint files.

caliber

The diameter of a gun barrel is known as its _____________.

how a firearms examiner compares 2 bullets

The examiner places both bullets under a comparison microscope, pointing in the same direction, and then rotates one bullet until a well-defined land or groove comes into view. When the examiner locates striation markings on this bullet, the other bullet is rotated until a matching region is found. When a matching region is located, the 2 bullets are simultaneously rotated to locate additional matching areas around the periphery of the bullets. The examiner uses striation markings to identify bullets because no 2 rifled barrels have identical striation markings.

less than

The liklihood of detecting GSR on swabs taken from living subjects more than 6 hours after a firing has occurred is _____ _________ the liklihood of detecting GSR within 2 hours of a firing.

rifling

The manufacture of a gun barrel requires impressing its inner surface with spiral grooves, a step known as ___________.

comparison microscope

The most important instrument for comparing bullets is the _____________ _________________. It is an indispensable tool for the firearm examiner because it allows 2 bullets to be observed and compared simultaneously.

SEM

The most promising technique of gunpowder residue detection for the immediate future is _________ primer residue detection.

class

The number lands and grooves is a ____________ characteristic of a barrel.

False

True or False: Cartridge cases are best marked at the base of the shell.

False

True or False: It is always possible to determine the make of a weapon by the bullet it fired.

False

True or False: Without the benefit of a weapon, an examiner can make an exact determination of firing distance.

semi-automatic

__________-_____________ pistols feature a removable magazine that is most often contained within the grips of the firearm.

firearms identification

___________ _____________ is a discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon.

single-shot

___________-_________ pistols can fire only one round, or shot, at a time. Each shot must be manually loaded into the chamber before firing.

single-action

___________-__________ firearms require the hammer to be manually cocked backward each time before the trigger is pulled in order to fire.

double-action

___________-___________ firearms cock the hammer when the trigger is pulled and then reload the firing chamber after the round is fired.

distance determination

____________ ________________ is the process of determining the distance between the firearm and the target, usually based on the distribution of powder patterns or the spread of a shot pattern.

ballistics

____________ is the study of a projectile in motion.

criminalists

___________________ can restore serial numbers removed or obliterated by grinding, rifling, or punching.

disadvantage of SEM

excessive operator time

characteristics an investigator should record about a firearm before unloading it

record the weapon's hammer and safety position as well as the location of all fired and unfired ammunition in the weapon. The cylinders and cartridges should be numbered because this information may be useful to determine the sequence of events, particularly in cases in which several shots were fired.

rifling methods

steel hook cutters (no longer used), broach cutter, button process, mandrel rifling/hummer forging

purpose of rifling

to increase speed and turning of the bullet as it leaves the barrel