Upload
adele-harrington
View
228
Download
10
Tags:
Embed Size (px)
Citation preview
Gunshot Residue Particle Analysis Technique
S.S. Baisoya
Central Forensic Science Laboratory Chandigarh
CFSL Chandigarh 2
Introduction
Gunshot residue particle analysis pertains to: Identification of bullet holes Estimation of range of fire
Linking the suspect with the firing of a gun-in-question
CFSL Chandigarh 3
Gunshot Residues When a firearm is discharged –
discharge products are expelled from its muzzle: -
Gases and vapours Particulate materials (inorganic &
organic) Burnt and unburnt gunpowder
particles Metallic chips
(collectively known as Gunshot Residues)
Gunshot residues disperse down the range (in and around the bullet hole)
Gunshot residues disperse in backward and lateral directions (falls on the hand, face or clothing of a person)
CFSL Chandigarh 4
Formation of GSR particles
When firing pin strikes percussion cap, it ignites the primer mixture
Primer mixture vaporizes due to high Temperature, condense to droplets due to super-saturation,
Passes through various meta-stable stages of Temperature and Pressure, grow into bigger sizes by coalescence,
With the expansion and cooling, rapid condensation of droplets, freeze in their existing form of tiny particles
CFSL Chandigarh 5
Sources of Gunshot Residues
Primer consisting of: Initiating explosive, Oxidizing agent, Fuel, & Sensitizer
(Initiating explosive: Lead stephnate, lead azide, mercury fulminate Oxidizing agent: Potassium chlorate, barium nitrate, lead nitrate, lead peroxide and other components such as calcium silicide, lead thiocynate, aluminum powder, zirconium powder, magnesium and titanium)
Propellant Single base powders and double base powders
(Nitro-cellulose, nitro-cellulose along with nitro-glycerin) Additives
Stabilizer, plasticiser, coolants, flash inhibitors, lubricants, moderants etc.
Metals of bullet, cartridge case and barrel
CFSL Chandigarh 6
GSR Analysis Techniques Bulk analysis techniques: - Neutron activation analysis
and atomic absorption spectroscopy Total quantity of elements (Pb, Ba, Sb) estimated The measured amount should be more than the threshold limits Very low success rate of about 10% Lack of specificity, time consuming and costly
Particle analysis technique: - Technique using SEM-EDXA
Morphological analysis and elemental analysis simultaneously Morphology in combination with elemental composition makes
particles unique, so no threshold limit Superior success rates Automated GSR software reduced the problem of time and
manpower consumption
CFSL Chandigarh 7
GSR Technique in Casework
Equipment: SEM coupled with EDX/WDX, Automated GSR analysis software
for particle detection/ classification
Software for EDX/WDX automation Sputter Coater
Sampling procedure: Using GSR kit
Method of experiment: Sample pre-treatment Autorun of sampling stub
Protocol: The protocol is based on the
Aerospace recommendations
CFSL Chandigarh 8
Sampling Each GSR kit contains
Instructions A pair of rubber gloves Labels Two sample vials
Each vial contains adhesive coated aluminum stub mounted on the base of a rubber stopper
Stub pressed and lifted on the surface being sampled
Hand Face Clothing
CFSL Chandigarh 9
Identification of GSR Particles
Surface Morphology Varying size (0.1m - 10m,
occasionally up to 55m or even more)
Predominately spheroid (60-70%), also irregular, cluster and flake
Elemental Composition Varying elemental composition (Pb,
Ba, Sb, & elements such as Cu, Fe, Zn, Al, Si, S, K & Ca)
Distributions of elements (Pb-Ba-Sb) corresponds to various meta-stable stages of T & P
CFSL Chandigarh 10
Particle Classification Recommendations of Aerospace Corporation (1977)
Unique Particles (with no known source other than GSR) Pb-Ba-Sb, Ba-Sb (at least one component is a major peak)
Typical Particles (considered to be typical of GSR but not unique to it) Ba-Ca-Si (S is absent or trace), Pb-Sb, Pb-Ba (at least one
component is a major peak) Compatible Particles (commonly found in association with GSR, but
for which a wide variety of potential sources can be identified.) Pb, Ba, Sb (S is absent or trace), any combination of allowed
elements (Si, Ca, Al, Cu, Fe, S, P, K, Cl) Not GSR – Inconsistent with GSR and another source is known,
and Others – Inconsistent with GSR and source is unknown
CFSL Chandigarh 11
Detection of GSR Particles
Each element present in residues emits characteristic X-rays when bombarded with electrons in vacuum chamber of SEM
X-ray analyzer coupled with SEM detects X-ray quanta, records and prints X-ray spectral peaks automatically
It also classifies particles according to their elemental composition
The X-ray spectral printout shows all the elements present at the major and minor levels and their relative intensities
X-ray peak height and comparison criteria Major peak: 1/3 highest peak or higher Minor peak: > 1/10 but <1/3 highest peak Trace peak: 1/10 highest peak or less, but still clearly
identifiable
CFSL Chandigarh 12
Collecting X-ray Spectra EDX spectrum printout of a given unique particle will show all
elements present at major & minor levels, and their relative intensities. (if necessary, more than one spectrum may be taken)
Presence of Pb, Ba and Sb in a given unique particle should be documented by EDX spectrum showing the following peaks
Lead M1 L1 L1 L2
Barium L1 L1 L2
Antimony L1 L1
(If necessary, more than one spectrum may be taken) Caution is needed in case when the following peaks overlap.
Antimony-Tin-CalciumLead-Sulphur-MolybdenumBarium-titanium
(It may require to resolve the peaks further)
CFSL Chandigarh 13
Interpretation and Documentation
Interpretation of data The primary goal of the analytical analysis of a sample
stub is to determine the presence of a minimum of one unique particle required to state that GSR was detected on a given sample stub.
Documentation of analytical results Documentation of analytical result is very important
for court purposes, or it may involve legal problem. The systematic approaches in documentation will also
ensure to reliability of the analyst and the ballistic expert.
CFSL Chandigarh 14
Forensic Significance Once the presence or absence of GSR on a sample stub is
established through SEM-EDXA analysis. By examining morphology and elemental content of
individual particles and by consideration of particle population as a whole.
The established population may consist of GSR particles in addition to particles from other known and unknown sources.
The particle population detected must be consistent with what would be expected of a normal firearm discharge.
The variables that influence How the GSR was deposited, What type of surface it was deposited upon, and Conditions that the deposit was subjected to during the time
frame between deposition and sampling, will be subjected to change on a case to case basis.
CFSL Chandigarh 15
Reports Positive face and hand sample or positive face and negative hand
sample The person either fired a firearm, was in proximity to a firearm during
discharge, or was in contact with a source of GSR i.e. a recently fired firearm
Positive hand sample only or positive hand and negative face sample The person either fired a firearm, was in proximity to a firearm during
discharge or was in contact with a source of GSR Negative hand sample only or negative hand or face sample
It cannot be possible to determine whether the person fired a firearm or was in proximity to a firearm being discharged
Positive clothing sample Sampled clothing of suspect was in proximity to a firearm being discharged
or was in contact with a source of GSR such as a recently fired firearm Negative clothing sample
It can not be determined whether the clothing was in proximity to a firearm being discharged
CFSL Chandigarh 16
Conclusion
Detection of even a single unique particle on hand, face or clothing of a suspect using the particle analysis technique allows the investigator to establish conclusively whether the person has recently discharged a firearm or was in the proximity during firing or has come in contact with the discharged firearm.
GSR particles detection helps in the bullets holes identification and the GSR particle dispersion pattern helps in estimation of range of fire.
Thanks