Firearms Identification
 Determining whether a
bullet or cartridge was
fired by a particular
weapon
 Includes
 Bullet comparisons
 Restoring damaged serial
numbers
 Detection and analysis of
gunpowder residue
 Estimation of muzzle to
target distance
 Detection of gun powder
residues on hands
Gun Barrel Anatomy
 Gun barrel inner surface leaves
specific markings of bullet shell;
very important to gun
identification
 During production, gun barrels are
hollowed by drilling which leaves
striations on the inner barrel
 Bore—inner barrel
 Rifling—spiral grooves formed in
the bore
 Lands—raised portion between
the grooves in the bore
 Caliber—diameter of bore of a
rifled firearm; i.e. .22 inch caliber
or 9 mm caliber
Bullet Markings
 As bullets are fired through
barrel, the markings on the
barrel leave specific
markings on the bullet
 Test firings are done with
suspect weapons to see if
markings on new test bullets
match crime scene markings;
test firings are done box of
cotton or water to make
recovery easier
 Comparison microscope is
used to match bullet
markings
Bullet Analysis
Considerations
 Often much of bullet
markings are damaged at
impact; only piece of rifle
bore patterns are intact on
damaged bullets
 Barrel striations can be
worn down with many
firings
 Recovered bullet markings
can be used to determine
brand and caliber of
unknown weapon type
General Rifling
Characteristics File
 Some weapons have
microgrooving—8 to 24
grooves in rifle barrel
 FBI maintains a record of
Rifling characteristics such
as land and groove width
dimensions
Shot Guns
 Shot guns have smooth
barrels; not rifled barrels
 Not impressed with any
specific markings
 Fire small lead balls or
pellets
 By measuring diameter and
weight of shot recovered at
crime scene, size of shot
used in shell and gauge of
shot gun can be determined
 Gauge—size designation of
a shot gun
Cartridge Cases
 At firing, shell or cartridge
case pushed hard against
breechblock—rear part of
the barrel
 Shell is marked by contact
with metal surface of
breechblock
 Shape of firing pin may
leave markings; can be
individual character
 http://www.youtube.com/
watch?v=sBKJZTkbypo
Automated Firearms
Search Systems
 With the great increase in
automatic weapon use,
weapons are often used in
multiple crimes
 Bullet and cartridge surface
characteristics of weapons
from one crime can be
stored and accessed to
compare to shells or bullets
recovered at another crime
scene
 National Integrated Ballistics
Information Network
Ballistic Fingerprinting
 Information is being stored
from not only crime scene
weapons, but from all
weapons fired at test
samples
 Samples can be taken from
handguns before they are
sold so that if they are used
in a crime, data would be
available for ballistic
matching
Gunpowder Residues
 When firing, gunpowder is
converted to gas.
 However, powder is never
fully consumed
 Partially burned powders
are propelled toward the
target
 The distribution of
gunpowder residue around
the bullet hole permits
distance determination
Distance Determination

Very important in possible suicides to have gun fired
very close to body

Also, always measured in self-defense claims to see if
distance is viable for self-defense

Is especially helpful when weapon isn’t recovered to
have distance information from fired weapon

Compare victim’s patterns to sample patterns made
during test firing at white fabric or fabric like victim’s
clothing

If no gun is recovered for test firing, patterns are
analyzed

Close range firing leaves burnt fibers around bullet hole

Close-range shots may have a star-shaped tear pattern
called a stellate

http://www.youtube.com/watch?v=AVVEz8hpmos

http://www.youtube.com/watch?v=2kEh3Kgwhk0
Powder Residues on
Garments

All clothing must be analyzed for gunpowder
residue

Can be detected visually by characteristic color,
size, and shape

Sometimes gun powders are same color as
clothing and hard to detect

Sometimes blood covers up gun powder; so is not
as visible

Infrared photograph will enhance the contrast
between the powders and garments

Greiss test-tests for nitrites which are often
present in residue; transfer residue to chemicallytreated gelatin coated photographic paper; hot
iron is used to press paper onto target; chemical
treatments make nitrites visible

Sodium rhodizonate is sprayed over surface to
test for presence of lead; lead particles turn pink
and then blue violet
Primer Residues on Hands

During firing, gunpowder and primer
residues are blown back toward the
shooter as well

Traces of powders show up on the
shooting hand; So, can be figured out if
the hand recently fired a firearm

Dermal nitrate test—hot parafilm to
suspect’s hands with paintbrush; Dry
wax was removed and tested with
diphenylamine; bue color indicates
positive reaction for nitrates

Urine, fertilizers, tobacco, and make up
can all give test positive for nitrate
presence

More current tests measure for the
presence of primer residue on the
hands that fired a gun
Testing for Primer
Residues

Measure the presence of barium and antimony on
the hands of gun suspects

One test applies adhesive tape to the hands to
remove any residue; SEM is used to view particles;
best test for primer residue

Another test swabs both hands with 5% nitric acid
to collect any primer residues

Presence of barium or antimony shows recent
firing or handling of gun

Primer residues can be removed by washing
hands; has to be done less than two hours after
firing

Neutron activation analysis can be done to test
for barium and antimony

Flameless atomic absorption spectrophotometry
can be done as well

http://www.youtube.com/watch?v=WkcioQGfAgU
Serial Number Restoration
 Criminalist must try to restore
number when it has been
removed or obliterated
 Stamped on metal body or
frame with hard steel dies; hard
force allows dies to sink into
metal at prescribed depth
 Serial numbers can be restored
because imprint puts strain into
metal deeper than the
superficial letter imprints
 Surface is cleaned and treated
with etching agent; Agent
dissolves faster in altered area
than unaltered area leaving
imprint of number
Collection and
Preservation of Firearms
 Do not pick up in a way that
disrupts gunpowder residue
 Unload bullets from weapon
 When weapons are found,
positions and angles of
barrels and chambers must
be noted
 Bullets that are collected
must be handled gentler to
avoid damaging scratches on
surface that are vital for
analysis
Tool Marks
 An impression, cut, gouge, or
abrasion caused by a tool coming
in contact with another object
 Most often found at burglary
scenes where there is some
forced entry
 Often found on frame of door of
window in wood from screwdriver
or crowbar
 Examination of marks can tell size
and shape of tool; yield class
characteristics
 Only get individual characteristics
if tool has some wear mark or nick
that might help discern identity
Reference Samples
 Duplicating tool mark
impressions is difficult
 Reference marks are made
in soft metal surface like
lead
Collection of Tool Mark
Samples
 Entire object with marks is
collected as evidence (window
jam, door jam, car door, etc.)
 If too large to be brought back
to lab, marks are photographed
 Cast marks are made with
silicone
 http://www.youtube.com/watch
?v=ZD-KSGDFX_g
 Cannot try to fit suspect tools
into crime scene marks because
it may damage crime scene tool
impressions
Other Impressions
 Shoe, Fabric, tire
impressions are often left
at crime scenes
 Impressions must be
photographed
 Recoverable items are
taken back to crime lab
 http://www.youtube.com/
watch?v=KEyRE6KYbIs
Lifting Impressions
 When impressioned items
can’t be taken back to crime
lab
 Made in light deposits of
dust or dirt
 Lifting material is placed on
top of entire impression and
lifted
 Electrostatic lifting—mylar
film is placed on surface and
high voltage electrode is
used to transfer pattern to
film
Casting Impressions
 Photography first
 Then, casting of shoe and
tire marks in soil at crime
scene
 Class I dental stone, gypsum,
is used for impression castes
 Snow impression wax can be
used for lifting impressions
in the snow
 Latent blood tests can be
used to highlight foot
impressions in blood
Comparing Impressions
 Style, manufacture of shoes or
tires, size of shoe can be
determined from castings
 Can be matched to reference
samples
 Shoeprint Image Capture and
Retrieval—database in England
of shoe print information
 Bite mark impressions are very
important pieces of evidence at
crime scene—individual
characters
 http://www.youtube.com/watch
?v=thfHB5e51q8&feature=fvw