CH. 15
FIREARMS,
TOOLMARKS, AND
IMPRESSIONS
CH.
In
15 – FIREARMS, TOOLMARKS, AND IMPRESSIONS
2004 – 29,569 gun deaths in US
Suicides
account for 56% & homicides for 40%
Us
4.4 deaths per 100,000 compared to Germany with .45
per 100,000 and .015 per 100,000 in Japan
Forensic
guns
analysis is vital in order to solve crimes involving
Gunpowder
was invented in China in 200 AD eventually
leading to the development of modern weapons after the
propellant was refined and progress in metallurgy, physics,
chemistry, and armaments not to mention the continued
need to kill.
 TYPES OF FIREARMS
 Handguns
or pistols – designed to be held in one hand, easy to carry
& conceal, not as accurate as other firearms, limited to number of
bullets that are loaded
 Revolver
– usually 6 bullets are loaded into a cylinder, reloading is
by hand, shells are not ejected when spent
 Semiautomatic
– holds 5-19 rounds in a magazine/clip, shoots 1
cartridge every time trigger is pulled, ejects the spend cartridge
case & reloads automatically
 Rifles
- shoot more powerful cartridges than handguns, greater range
& better accuracy, longer barrel
 Shotguns
– similar to rifles, shoots packet of shot or spherical pellets,
inside of barrel is not rifled
 Air
guns or BB guns – shoots shot or pellets propelled by pressurized air
spring compression or a carbon dioxide cartridge
TYPES
OF AMMUNITION
Composed
of cartridge case, primer, propellant and a
projectile & varies based on the weapon
Base
of the cartridge contains the primer which is struck by
the firing pin of the gun igniting the gunpowder in the
cartridge case. Gas is created that pushes the projectile
out of the cartridge case, along the barrel, & out of the
weapon
Over
300 kinds of ammunition for handguns alone
Various
parts/pieces of the ammunition used as evidence
in an investigation.
 Can
be either class or individual
 BULLETS
 Bullets
made of lead & covered with brass, copper or steel.
 Armor-piercing
bullets made from steel or tungsten alloys coated with thin
layer of lead or copper/brass to prevent barrel wear
 Bullet
size is a measure of the diameter & expressed in inches and referred to as
“caliber.”
 Ex:
bullet measures 22/100 of an inch is a .22 caliber bullet
 Caliber
bore
 If
also corresponds to the inside diameter of the firearm’s barrel or
measured in metric – 9 mm – is approximately same size as a .38 caliber.
 Size
of a shotgun described by gauge & related to the weight of the lead
pellets or shot in the shell. Larger the diameter of a shotgun bore, the smaller
the gauge
 Single
pellet is called a slug.
BULLET
SHAPES
Bullets
come in different shapes, see Fig. 15.7, pg.
443
Bullets
with holes in the cone deform on impact to
decrease penetration & cause greater bodily
harm.
Flat-nosed
Weight,
lead bullets used for target practice
dimensions, shape & type of bullet are
class evidence
 Handgun
& rifle barrels are rifled to increase the accuracy of shooting
 “Rifled”
refers to the cylinder being machined to form a grooved
spiral inside the barrel to create a spin to the projectile, decreasing
wobbling in flight, increase accuracy.
Rifling
in the barrel produces “Lands” & “grooves” on a bullet
that twists either to the left or to the right
Lands
& grooves are class characteristics & used to identify
the make & model of a weapon.
 Striae
or scratches on a bullet created from wear patterns
 Scratches
resemble barcodes which create a unique kind of
“fingerprint” for the bullet
 Changes
 Problem:
the bullets from class to individual characteristics
many bullets are too badly deformed or fragmented to
be helpful.

THE CARTRIDGE
The
cartridge consists of the bullet & a case or
shell that contains the powder and a primer.
Case
made of brass or nickel-clad brass
Propellant
is smokeless powder
Combustion
products of the chemicals are
expelled from the ejection port, leaving
behind the presence of lead, barium,
antimony letting scientists know a weapon
was fired.
 Cartridge found at a crime scene is both class & individual
evidence.
 Class
evidence includes:
dimension
imprint
on the base or head stamp
whether
 Individual
of the shell casing
it is rim or centerfire
evidence includes:
impressions
ejection
on the firing pin when it strikes the primer case
of cartridge being pulled out of the firing
chamber by a hooked extractor & thrown clear of the
chamber by the ejector.

DISTANCE FROM TARGET
Knowing
the distance from muzzle to target can aid
in the reconstruction of the event.
When
a bullet leaves the muzzle of a weapon,
unburned particles are carried along, plus
combustion products of the propellant, which
spreads out over distance
Greiss
test will chemically convert the nitrites in
gunpowder residue into a colored product
Muzzle
very close or pressing against the target
causes burns & deposits a lot of soot
 GUNSHOT RESIDUE
 The
primer ignites the powder charge, hot gases that propel the
bullet from the firing chamber blow out from the ejector port & the
muzzle.
 Blowback
disperses combustion products of the primer back to the
shooter’s hand, plus blanketing the area alongside & behind the
weapon
 Presence
of lead, barium, & antimony is indicative that a
weapon was fired, but the particles may not necessarily be
traceable to the shooter because it is widespread & easily
transferred
 The
term “gunshot residue” (GSR) refers to the ejector particles,
combustion residues of the powder & any unburned powder
particles.
GUNSHOT
RESIDUE
Well
equipped crime lab will be able to confirm GSR
residues from a shooter’s hand using sophisticated &
expensive instruments.
Blowback
contamination is a problem
Tests
done on top of the thumb & forefinger & then
compare it to the palm helps in interpretation
No GSR on the palm of a shooter, if palm is sprayed with a
specific solution & using a UV light it will show the imprint of
the pistol grip.


Color of the fluorescence indicates the type of finish on
the metal or pistol grip.
GUNSHOT
RESIDUE
Bureau
of Alcohol, Tobacco, Firearms & Explosives’
National Integrated Ballistic Information Network
(NIBIN) maintains a forensic data base containing
information on bullets & cartridge casings retrieved
from crime scenes & test-fires of guns found at crime
scene or on a suspect.
Now
contains over 1, 286,5000 pieces of evidence
More
than 20,300 hits (matches of evidence with
other evidence) have been registered
 Read
in your textbook pages Case 15.1: The Case of People v.
Contreras, pgs. 454, 455 & 456.
 Discuss
 What
do you think happened
 Where
 Was
was the cartridge case?
it ever looked for?
 What
 Why
with your group the following questions:
was Ms. Contreras’ state of mind when she called 911?
did she confess, yet not know what she did with the rifle?
 Why
wasn’t GSR tested around the bullet hole to determine the
distance of travel?
 Why
didn’t the state consider a shot from outside?
Read
the information at the top of pg. 457 &
discuss the following questions?
Do
you think a thorough & accurate
investigation was conducted? If not, state
what you felt was missing or done incorrectly.
After
reading the case study, what questions
do you still have?
What
do you feel about the statement:
“Justice & truth may not be synonymous.”
TOOLMARKS
Many
different tools are used in many
different ways in many crimes
Ex:
screwdriver used to pry open a door.
 Toolmarks
are caused when the tool is
used against a softer material leaving
behind impressions.
Ex:
metal screwdriver used against the
wood frame of a door
TOOLMARKS
Toolmarks
evidence
can be both class & individual
Class
evidence–features of the tool itself
– its shape & size
Individual
evidence – tool over time
becomes worn or damaged acquiring
unique markings that will differentiate it
from other similar tools
 TOOLMARKS
 Toolmarks
sketched
associated with a crime are 1st photographed &/or
 If
the tool is left at the crime scene, it is taken to a lab for
further examination
 If
tool is not left behind, a cast is taken of the mark with either
silicone, plaster, or clay material
 Next,
using the cast, a 3 dimensional replica is made.
 Class
of tool needs to be identified, so that police know what
to look for among the suspects
 Recovered
tools are compared to the toolmark evidence,
hopefully finding unique characteristics to achieve a match
IMPRESSIONS:
FOOTWEAR MARKS OR SHOEPRINTS
Name
at least 3 different mediums where shoeprints could
be used as evidence.
Information
Direction
Point
that footprints can reveal about the crime:
of approach & departure
of entry & exit
Mode
of entry
Sequence
Class
of events that took place
& perhaps individual evidence linking suspects to
the scene

IMPRESSIONS:
Standard
method of documenting impression
evidence is photography
Oblique-angle
viewing can make a difference – see
Fig. 15.33 on pg. 461
 Methods
of collecting & preserving impressions:
Casting
Electrostatic
surface
Chemical
or adhesive lifting if imprint is on a hard
enhancement – dye on a bloody shoeprint

IMPRESSIONS:
Matching
shoeprint evidence to a shoe involves class
characteristics
Manufacturer,
type, model & size
Individual characteristics when footwear outsoles
becomes worn & damaged

SoleMate is a commercial database that contains
manufacturer, date of market release, image or offset print
of the sole & pictorial images of the shoe itself.

Contains
over 12,000 sport, work & casual shoes
TreadMark
is a database that stores & compares imprints
from a crime scene.

IMPRESSIONS:
Personal
Traits
Footprints
can sometimes tell you information
about the person.
Ex:
length of stride & the way the footprint
has dug into the ground can suggest
running
Walking
gait, the length of stride may be
related to the height of the individual.

TIRE TREADS
Tread
marks in tires are treated similar to
footwear marks due to the fact that both
are mass produced
Class
characteristics include: design, size,
type & model
Individual
characteristics include: wear
and damage causes defects used to
individualize the tire
TIRE
TREADS:
Vehicles
are often involved in crimes & many
times tire marks are the only way to identify a
vehicle.
Impressions
left in mud, dirt, dust or imprints left
on a smooth surface by a moist or dirty tire can
be photographed & collected using the same
techniques as those used for footwear.
Vehicles
very heavy so tire impressions can
also be found on a body

TIRE TREADS:
Data
bases for tires contain information on tread designs,
manufacturer, date of market release, wheelbase
(distance from the center of the front wheel hub to the
center of the rear wheel) & stance (distance from the
centerline of the right tire to the centerline of the left tire)
Any
changes to a tire’s tread, like bald spots, cuts, etc.,
could be seen in a cast impression
Tires
containing caked soil or wedged rocks in the tread
can provide information on periods of time and is referred
to as a “temporary chacteristic.”
Skid
marks can be used to reconstruct an accident, hit &
run, & tire failures in moving vehicles
BITE
MARKS:
Bite
mark evidence is common with victims of domestic
violence & in some case an assault or sexual attack
Everyone’s
teeth that are slightly different shapes,
widths & arrangement.
Chips,
fillings, crowns & caps make a person’s teeth
unique.
Odds
of 2 people with the same bite marks with a full
set of 32 teeth is 2.5 billion to 1.
Bite
marks were a prime piece of evidence to convict
serial killer Ted Bundy

RESTORATION OF SERIAL NUMBERS:
Many
items have serial numbers & are
assigned so that ownership can be
traced
Ex:
VIN # on a car
Criminals
try to obliterate the
identification # - usually by grinding it
off
 RESTORATION OF SERIAL NUMBERS:
 Process
to create the identification number:
 Metal
is stamped or punched creating a crystal structure
beneath the impression that is deformed
Area
will react to an etching solution more readily than
the surrounding area
 Restoration
of identification number:
 On
metal – 1st polish the area with emery cloth & repeated
swabbing with an acidic chloride solution will retrieve the
numbers
 Retrieving
numbers can also be done on wood, plastic &
precious metals