Transcript Firearms, Tool Marks, and Other Impressions

Firearms, Tool Marks, and Other
Impressions
Objectives:
1. Describe techniques for rifling a barrel.
2. List the class and individual characteristics of bullets
and cartridge cases.
3. Explain the utilization of the comparison microscope
for the comparison of bullets and cartridge cases.
4. Distinguish caliber from gauge.
7/17/2015
Created by C. Ippolito April 2008
1
Firearms Identification
• concerned with determining whether a bullet
or cartridge was fired by a particular weapon
– bullet  gun
• structural variations
• irregularities
– scratches & nicks
– breaks & wear
• more than bullet comparisons
–
–
–
–
7/17/2015
weapons operation
restore obliterated serial numbers
detect & characterize GSR
determine muzzle-to-target distance
Created by C. Ippolito April 2008
2
Gun Barrel Manufacture
• made from solid bar
– hollowed by drill
• random marks left
– followed by rifling
• grooves on inner surface
– “twist” bullet for straighter, more accurate path
• rifling methods
– hook cutters – rotated – forms spiral groove – 1 at a
time
– broach cutter – concentric rings – simultaneous cuts
all
– button process – metal plug compresses sides
– mandrel process – barrel hammer from outside
down
7/17/2015
Created by C. Ippolito April 2008
3
Gun Barrel Terms
• Bore
– the cavity inside the barrel
• Rifling
– spiral grooves in bore
• spins projectile
• Groove
– cut/low-lying parts of rifled bore
• Land
– uncut/raised parts of rifled bore
• Caliber
– diameter of the bore
• hundredths of an inch (.22)
• millimeters (9mm)
7/17/2015
Created by C. Ippolito April 2008
4
Bullet Markings
• Class Characteristics
– lands
– grooves
– twist direction
• General Rifling Characteristic File
– FBI data base of class characteristics
• Individual Characteristics
– striations
• fine lines caused
– minute imperfections on cutters
– steel chips from cutters
• Comparison Microscope
– tool used to compare bullets
7/17/2015
Created by C. Ippolito April 2008
5
Shotgun Barrel
• smooth bore
– groove would spread
pellets
• gauge
– diameter of barrel
– # of lead balls with
diameter = to bore of
barrel that would
weigh 1 lb
7/17/2015
Created by C. Ippolito April 2008
6
Comparison of Cartridge/Shotgun
Shell
7/17/2015
Created by C. Ippolito April 2008
7
Cartridge/Shell Markings
• Breechblock
– rear part of barrel
– marks base of cartridge/shell
• Firing Pin
– strike mark on base of cartridge/shell
• Ejector/Extractor
– mechanism that removes cartridge/shell from
chamber
• leaves unique striations
7/17/2015
Created by C. Ippolito April 2008
8
Firearms, Tool Marks, and Other
Impressions
Objectives:
1.
2.
3.
4.
7/17/2015
Explain the NIBIN data test system.
Explain the procedure for determining at what distance from a
target a weapon was fired.
Describe the laboratory tests utilized for determining whether an
individual has fired a weapon. Emphasize the limitations of the
present techniques.
Explain why it may be possible to restore an obliterated serial
number.
Created by C. Ippolito April 2008
9
Automated Firearm Search Systems
• DRUGFIRE (FBI)
– unique markings on cartridge cases
– microscope images captured and digitalized
• Integrated Ballistic Identification System (ATF)
– Bulletproof
• bullet analyzing module
– Brasscatcher
• cartridge analyzing module
• National Integrated Ballistic Identification System
– 1999 the two systems combined
7/17/2015
Created by C. Ippolito April 2008
10
Gunpowder Residues
• Distance determination
– distribution of powder/pellets
– calculate firearm distance from target
• Handguns and Rifles
– 1” or less
• heavy smoke stains
• loose fibers/melted fibers
• star-shaped tear surrounded by smoke
– 12”-18”
• halo of smoke stain
– 25”-36”
• scattered gunpowder particles
– ball powder cartridges can extend to 6’-8’
– > 3’
• bullet wipe
– carbon, dirt, lubricant which wipes off surface of bullet
7/17/2015
Created by C. Ippolito April 2008
11
GSR Patterns
7/17/2015
Created by C. Ippolito April 2008
12
GSR Patterns
•
•
•
•
3”
9”
15”
21”
• Greiss test
– shows nitrites
• Sodium rhodizonate Test
– turns lead particles pink then violet
7/17/2015
Created by C. Ippolito April 2008
13
Primer Residues
• Dermal Nitrate Test
– paraffin wax treated w/diphenylamine
• blue color w/nitrates
• Primer Test
– looks for:
• lead styphate
• barium nitrate
• antimony sulfate
– SEM Testing
– Neutron Activation Analysis
– Atomic Absorptive Spectrophotometry
7/17/2015
Created by C. Ippolito April 2008
14
Serial Number Restoration
• detects strain in metal crystals
– can be “re-etched”
• HCl + copper chloride + water for steel
7/17/2015
Created by C. Ippolito April 2008
15
Firearms, Tool Marks, and Other
Impressions
1.
2.
3.
4.
7/17/2015
Objectives:
List procedures for the proper collection and preservation
of firearm evidence.
Explain how a suspect tool is compared to a tool mark.
Explain the forensic significance of class and individual
characteristics to the comparison of impressions.
List some common field reagents used to enhance bloody
footprints.
Created by C. Ippolito April 2008
16
Collection & Preservation of Firearms
• Safety – unload any ammo
– note hammer/safety position
– note location of fired/unfired ammo
• Revolver
– note chamber position
• note cartridge/casing in chamber w/position
• each round in own box
• Automatic
– remove magazine – test for prints
• Water recovery
– ship weapon with water covering weapon
7/17/2015
Created by C. Ippolito April 2008
17
Collection and Preservation of Ammo
• Must save class/individual markings
–
–
–
–
7/17/2015
free bullets by breaking away material
use only plastic tools
scribe with initials
leave trace materials on bullet
• paint, fibers, etc.
Created by C. Ippolito April 2008
18
Tool Marks
• indented impressions class characteristic
– all tools show microscopic irregularities from
their manufacturing
• indented impressions individual
characteristics
– microscopic irregularities from damage and
wear
7/17/2015
Created by C. Ippolito April 2008
19
Preserving Impressions
• photograph
• Lifting Impressions in Dust/Dirt
– electrostatic lifting device
• Casting Impressions
– dental stone (gypsum)
– Snow Impression Wax
7/17/2015
Created by C. Ippolito April 2008
20