Up-range GSR
aka Primer residue: sets on hand and clothing of shooter and nearby surfaces
-used to determine whether a person has had contact with a firearm or ammunition
Down-range GSR
aka muzzle GSR: on surfaces that have encountered "business end" of a fired gun.
-used for distance determination
location of GSR type on firearm
What is a primer
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common primer components
1. explosive: lead-styphnate
2. Fuel: Antimony sulfide
3. Oxidizers: Barium nitrate
-some non-toxic primers are lead and/or barium-free
gunshot residue particle characteristics
A. small (1-10 um)
B. Lead (Pb), Barium (Ba), Antimony (Sb),
C. molten, non-crystalline (usually spherical) structure
Characteristic GSR particle composition
- 3 components PbBaSb
-2 component particles consistent/indicative with GSR but may be from other sources
-May contain other elements from the primer, bullet, cartridge case,
-exceptions: Some .22ca ammunitions do not have Sb or Non-tox/"lead-free" ammunitions
Primer GSR Collection
1. tape-lifting it off the hands or clothing of a suspect
2. Commercial GSR kits should be used (Carbon-tape adhesive lift, Mounted on an aluminum stub for SEM/EDS analysis)
Primer GSR Analysis method
Scanning Electron Microscopy / Energy Dispersive Spectroscopy (SEM/EDS).
SEM
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SEM: Secondary Electrons
knocked out" of the specimen and collected by a detector.
An image of the surface of the specimen is generated.
SEM: Backscattered Electrons
electrons from the incident beam interact with the specimen, bounce back and are collected by a detector.
Produces an image where "heavier" elements are brighter and "lighter" elements darker.
EDS
When secondary electrons occur from SEM an X-Ray is emitted and collected by EDS detector
The energy of the x-rays used to determine what elements are present in the specimen, creating an x-ray spectrum
Steps of GSR analysis
The GSR stub is mounted in the SEM
Automated analysis searches for bright particles that contain PbBaSb
The analyst then revisits the particles, takes an X-Ray Spectrum to confirm elemental composition and takes a picture.
What information can primer gunshot residue REALLY tell you?
The benefits & limitations of primer GSR evidence are not well understood by the public, law enforcement, and district attorney's.
True or False: If a person has GSR on his/her hands, this proves that he/she has recently fired a gun.
False--The Presence of GSR Indicates That:
-subject may have discharged or been near the discharge of a firearm
-may have handled firearm or ammo
-been in contact with surface bearing GSR
True or False: If a person does NOT have GSR on his/her hands, this proves that he/she has not recently fired or handled a gun.
False--The Absence of GSR Indicates that:
-may not have discharged firearm
-may have discharged firearm but no GSR particles on sampled area--or were removed before sample collected
Facts about GSR
- used to determine if a person was present in an environment with gunshot residue (if someone was shot= in GSR environment)
studies show:
- gunshot victims can have GSR up to 50 feet down-range
- majority homicide gunshot victims have GSR on them
-many suicides do not have GSR on them (environmental conditions, movement of body)
True or False: Primer GSR can be used to distinguish between a suicide and a homicide.
FALSE
Problems with GSR analysis
-analysis is the easy part, reconstruction of how gunshot residue got there is the hard part
-Contamination/Secondary Transfer Problems: Police officer's hands, patrol vehicle, jail
-Fleeting Evidence: Hand washing, activity causes GSR to fall off.
How are problems with GSR minimized?
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Why do we do GSR analysis if the interpretation is so limited?
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Downrange" GSR Examination
When a firearm is discharged & the bullet strikes a surface, GSRs are deposited, particularly at close range.
residues and pattern they are deposited may be reproducible (type of firearm, ammo, distance discharged)
some residues visible, some need chemical treatment
What information can we obtain from down-range residues?
If a "defect" is consistent w/ a bullet impact.
Muzzle to Target Distance Estimation
(Max possible distance, Min-Max range)
composition of down-range residues
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down-range GSR Visual & Microscopic exam
Hole in the target / material
Presence of Bullet Wipe
Ripped or torn material in a stellate pattern (consistent w/ contact shot).
Down-range GSR Chemical Treatments
1. modified Griess test
2. Dithiooxamide Test (DTO)
3. Sodium Rhodizonate Test
Nitrite Residues
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Modified Griess Test
-for nitrite residues
-The patterns increase in diameter & decrease in density as the distance increases.
-At greater distances no nitrite residues will be deposited (this = Max muzzel-to-target distance)
-Evidence treated with mod-griess is compared to a succession of known distance test fires (also treated with mod-griess)
_______________ should always be used when making distance determinations
#NAME?
Vaporous Lead Residues
This type of residue is projected from the muzzle of the gun as a cloud-like array.
Projected only to a particular maximum distance.
Characteristically deposited at closer ranges
chemically detectible with Sodium Rhodizonate (SoRo)
Sodium Rhodizonate (SoRo) Test
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What is a bullet wipe?
-visible ring around the perimeter of a hole consisting of copper-bearing or lead-bearing residues
-positive results for presence of bullet wipe are consistent with bullet passage (good for holes in objects with no particulate residues)
-commercial "test kits" available (lead=SoRo, diphenylamine---copper=DTO)
Dithiooxamide Test (DTO)
Chemically specific test for the presence of copper. (+ bullet wipe=bullet passage)
Copper-jacketed bullets represent a considerable %age of ammunition evidence in most criminal cases.
Shot Patterning
-firearms that fire multiple pellets (shotguns, "snake shots")
-pellet patterns measured distance >>> residues distance determination
-dependent on reproduction of physical environment (must have suspects firearm, ammo ID'd and duplicated)
Shot Patterning - Examination
1.Visual examination
2. Processed for Nitrite Compounds
Distinct difference between shot pattern distance determination vs. other firearms:
Distance determination is based on the size of the shot pattern & the pattern reproduction
Establishing a Distance Determination Range
- range of distance for the specific evidence pattern
- Range ~ 1 ft wide (must account for variations in ammo type, evidence handling)
- appropriate range: greater distance-->larger stated range
-must be within confines of test fires
Steps for Distance Determination Range
1. use suspect's firearm and duplicated ammo to create known-distance test fires
2. determine possible min and max extremes of range
3. verify extremes with 3 or more test firings
Goal of known test firings
reproduce the shooting incident as best as possible when doing known distance test firings.
-important to use same firearm and the same/similar ammo as shooting incident
shotgun Choke
-tapered constriction of the shotgun barrel's bore at the end of the muzzle
-determines and shapes the spread of the pellets to gain better accuracy and range/distance
Gunshot Wound Categories
1. Contact
2. Near contact
3. Intermediate
4. Distant
Hard Contact Wound
Muzzle of firearm is jammed "hard" against skin--skin envelops the muzzle (if force is hard enough may leave a muzzle imprint)
Immediate edges of wound are seared by hot gases of combustion and blackened by soot embedded in the seared skin---cannot be completely removed either by washing or scrubbing.
Basic components of gunshot wounds
A - Reddish ring of abrasion.
B - Bullet wipe caused by the fouling of the bullet in the barrel.
C - Small hemorrhagic marks (stippling/tattooing) on the skin produced by the impact of propellant particles.
D - Soot produced by burning propellant, which contains vaporized metals from the primer, bullet and cartridge case.
loose contact wound
The muzzle of the firearm is held lightly
against the skin.
Gas preceding the bullet and the bullet indents the skin, creating a temporary gap.
Soot carried by the gas is deposited in gap creating a band around the entrance.
This soot can be wiped away easily.
near contact wound
Muzzle not actually in contact with skin, but is close enough to that propellant does not have time to disperse and mark skin with stippling
Angled Contact Wound
The barrel is held at an acute angle to the skin so the complete circumference of the muzzle is not in contact with the skin.
Gas and soot escaping from the gap produce an eccentrically arranged pattern of soot.
Incomplete Contact Wound
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Intermediate-range gunshot wound
Muzzle of firearm held away from body at time of discharge but close enough that propellant particles produce Tattooing.
Gradual transformation from near contact to intermediate wounds.
Once Tattooing is visible around the entrance wound it becomes an intermediate-range wound.
Distant Gunshot Wound
Surrounded by a reddish zone of abraded skin (the Abrasion Ring.)
Abrasion Rings occur when the bullet abrades the edges of the hole as it indents and pierces the skin.
Not caused by the rotational movement because a bullet makes one complete rotation in 8 to 12 inches in horizontal travel.
Components of a shotgun ammo
-primer
-propellant powder
-wad
-casing
-projectile (shot=load of pellets--slug=1 solid "bullet")
shotgun slug
At close range, the shotgun is the most formidable and destructive of all small firearms.
A slug weighs approximately 402 grains, has a muzzle velocity of 1600 feet per second and a muzzle energy of 2485 ft pounds.
A .223 caliber (5.56 x 45 mm) bullet has a weight of 62 grains and a velocity of 2800-3280 feet per second and a muzzle energy of 1303 ft pounds.
ammunition design: cartridge
composed of a metal (usually brass) case resistant to corrosion and pressure, a propellant charge, a projectile or bullet, and a primer
ammunition design: bullet
- projectile component of ammo designed to seal in propellant gas and engage in rifling
-caliber: bullet diameter in inches (forty-five=.45 in)
-grain: bullet (only) weight
-common bullet composition: lead (soft, low melting point, light-weight)
full metal jacket ammo
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hollow point bullet
has cavity at tip where lead expands out into a mushroom shape upon impact
-greater stoppage power against soft material (human skin)
ammunition design: propellant
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ammunition design: primer
metal cup containing primary explosive inserted into base of cartridge
-primary explosive material sensitive to impact--firing pin crushes explosive, hot gas and sparks ignite powder propellant
ammunition design: magazine
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centerfire vs rimfire
center: firing pin hits primer located in center of cartridge base(shot shells are a type of center fire)
rimfire: firing pin strikes rim of cartridge base, primer located in rim
rimfire cartridges
Weak
� Reliability issues
� Non-reloadable
� Cheap
centerfire cartridge
Much stronger design
� Reloadable
Nominal versus specific caliber
Nominal caliber refers to a family of cartridges of similar bullet diameter
- Specific caliber refers to a particular cartridge designation share common physical characteristics allowing for interchangeability
(bullet diameter, allowable range of bullet weights, case and cartridge lengths, case and rim diameters, and peak pressures.)
Headstamps
� Commercial headstamps generally list specific caliber. Military headstamps often do not.
steps for bullet discharge
1. squeeze trigger
2. firing pin strikes primer--->primer ignites propellant powder
3. powder creates pressure--->pushes bullet down barrel
4.bullet spirals down bore, leaves through muzzle
steps for firearm use: putting a round in the chamber
1. feeding: positioning cartridge in position to enter chamber (manual or magazine loading)
2.Chambering: inserting cartridge in chamber
3. locking:The firearm's mechanism locks the cartridge in the barrel to contain the pressure of firing
steps for firearm use: cartridge removal
7. extraction:Removal of the cartridge case from the chamber by an extractor
8. ejection: Mechanical ejection from firearm
accomplished via an ejector.
9. cocking: Retracting of a hammer or striker against spring tension (manual or automatic)
firearm parts used for loading cartridge in chamber
a. slide: moves backwards to remove cartridge from magazine, forward to load cartridge in chamber.
b. hammer: gets pushed back/cocked by slide moving backwards
c. barrel: moves with slide--->moves back and down to accept round--->straight back to firing position
d. locking lungs: secure slide and barrel for firing
firearm parts for firing a cartridge
a. firing pin: strikes primer of cartridge
b. trigger: releases hammer by pushing on disconnector and sear
C. sear:controls hammer movement
d. disconnector: connect trigger to sear, breaks the connection so sear can return hammer to firing position without waiting for trigger
e. main spring: tension for hammer
barrel rifling
spiral grooves in barrel cause cartridge to spin (increases stability and accuracy)
firearm parts for cartridge ejection
a. extractor: has notch that fits cartridge ridge--->pulls it backward with slide
b. ejector:small ramp that pushes cartridge upward
over 90% of crime guns are....
handguns
repeating firearms
have magazines
-boxed or tubular
-fixed or removable
shotguns
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repeater shotgun types
a. Pump: fixed tubular magazine
b. semi-automatic: fixed tubular magazine
rifles
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single shotgun types
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rifle types
same as shotgun
repeater shotguns
magazines tubular or boxed
handgun categories
1. pistols (automatic repeating)
2. revolvers (manual repeating)
revolvers
single action
double action
single action
hammer must be manually cocked and before each shot to rotate the cylinder/accept magazine cartridge
double action
uses a long pull of the trigger to cock the hammer, rotate the cylinder/magazine cartridge, and fire the piece. Repeated shots may be fired by repeatedly pulling the trigger until all rounds have been fired
pistols
single action or double
glock safe action
trigger safety: push down on mini trigger
firing pin safety: pushed down on side of glock with thumb
drop safety: grip pressure
firearm and toolmark analysis case flow
1. inventory
2. examine firearm
3. determine firearm ammunition
4. microscopic examination of test fires
firearm examination
1. for trace evidence
2.note markings, serial number, unique features
3.safe function
firearm ammunition determination
1. documentation of ammo physical components
2. choose appropriate ammo for test fires
3.test fire
microscopic examination of firearm test fires
1. determine class (manufacturing design factors /group features) and individual characteristics(imperfections/irregularities during or after manufacture)
class and individual characteristics of evidence
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class characteristics
Color, cross section, length, hardness
Individual Characteristics of ammunition
striations on bullets
Subclass
Some manufacturing techniques can produce
imperfections that carry over to multiple
workpieces, producing marks that are not
unique to a single tool.
class charact. of ammunition
breech marks, firing pin impressions, extractor marks, ejector marks, number of grooves, direction of twist, and width
Toolmark Identification Theory
a. tool= a hard object that comes in contact with a soft object and leaves a toolmark
b.will have unique microscopic characteristics (class and indiv)
c. charact. will leave class and indiv. characteristics on surfaces
d. may be repeatable or identifiable
Victor Balthazard
Developed method for comparing individual
characteristics on fired ammunition components using enlarged photographs.
Stielow Case (1915)
- farmer and housekeeper murdered
-ammo=22 rimfire
-2 suspects: Stielow and Green---Stielow lied about have a 22 revolver
-revolver identified as murder weapon by "Dr." Hamilton--->Stielow sentenced to death
-Charles Waite reviewed Stielow case after two people confessed
-Barrel condition/microscopy proved revolver hadnt been fired in four years--->Stielow pardoned
Calvin Goddard
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saint valentines day massacre
-goddard starts crime lab in Chicago
-Identified murder weapons as one 12-Gauge shotgun and two Thompson Submachine Guns.
- Eliminated all of the Chicago Police Department's Thompson Submachine Guns
-Two Thompson's seized from Fred Burke ID'd to Saint Valentine's Day Massacre and murder of New York mobster Frankie Yale
Bullet Examination Theory
#NAME?
Cartridge Cases as Evidence
� Generally not left by revolvers
� No high speed impact
� May exhibit marks from 8 or more tools, i.e.
different parts of the firearm.
� Striated marks and impressions
Sources of Marks on
Cartridge Cases
Breech face, firing pin, firing pin aperture, chamber, ejector,
ejection port, extractor, magazine
Why document bullet
strikes?
Can help place shooter.
Helps investigators and juries visualize a scene
Theory negation
General crime scene reconstruction
Labeling Bullet Strikes
Use letters to designate trajectories
Each bullet strike in a trajectory designated
with a letter and a number (A1, A2, etc...)
Describing Bullet Strikes
described by measuring its distance from a fixed point in three dimensions (left to right, up and down, front to back)
measure angle
simple sketch (ref point with x,y,z coordinate designations and N,S,E, W)
table designating measurement coordinates
Describing Trajectories
can be visualized and measured using probes.
Trajectories can be extended from the probes
using string or lasers.
Determination of Projectile Paths:
Probe and String Method
a.Two Points of Reference: bullet path more accurately determined in two or more surfaces (sheetrock)
b. probe used to connect two reference points (can be different diameters)
c. colored and appropriate length dowels as probes for photos (photograph rods from all angles)
d. exits should be photographed from side view with horizontal ref line
probes
allow direct measurement of horizontal and vertical angles to better describe trajectories (direct measurement preferred over calculated angle)
calculated angle of bullet path: tools
1. protractor
2. inclinometer
types of angles for bullet path
elevation: vertical angle
azimuth: horizontal angle
Bullet Path for Scene Reconstruction
1.Provide Visualization / Illustration for
the official case record, for court, etc...
(show trajectory paths, entrance...exits, direction)
Leica Scan Station
To scale
3D Scans w/ trajectory rods in place demonstrate
shooter position.
Provide accurate angles and measurements
Trajectories can be extrapolated to determine potential shooter position
deflections
issue in bullet trajectory determination (bullet changes path when it goes through glass)
ejection pattern analysis
1. crime scene reconstruction (shooter position vs target)
2. search crime scene for cartridge cases
3. ejection pattern tests (initial contact and final contact with resting surface)
Consideration of impacting surfaces on ejection pattern in area of shooting scene.
1. type of contact surface (hard vs soft for bounce)
Limitations of Ejection Pattern
Determination: variables
The firearm
The ammunition
The height and orientation of the firearm
The nature of the receiving surface or surfaces
Position and location of intervening objects
The more of these variables that can be controlled, the more confidence the investigator can have in reproducing a representation of ejection patterns
possible disturbances that effect ejection pattern
Rolling of cartridge cases on inclines
Blowing wind
Post shooting activity of participants involved in incident
Post incident activity by citizens and/or moving traffic
Post incident activity of emergency personnel
Post incident activity by investigative personnel
methods of collection for impressions
1. best: collect item/print
2. lift print (gel, tape, electrostatic)
3. photograph
impression characteristics for crime reconstruction
a. connecting suspect
b. direction
c. type of shoe/tire
d. left or right, rear or front
e. crime relation
value of impression
1. ID shoe/tire
2. elimination
3. sizing (range)
4. tread design
5.solemate database
prints vs impressions
prints: 2D
impressions: 3D
elimation prints
anyone there before u that could have left prints
test prints
vaseline on shoe
paper clean, level, nontextured surfce
detecting prints
visible
oblique light and ALS