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Gunshot Residue Particle Analysis Technique

Gunshot Residue Particle Analysis Technique. S.S. Baisoya Central Forensic Science Laboratory Chandigarh. 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.

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Gunshot Residue Particle Analysis Technique

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  1. Gunshot Residue Particle Analysis Technique S.S. Baisoya Central Forensic Science Laboratory 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 (0.1mm - 10mm, occasionally up to 55mm 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) • UniqueParticles (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 Ma1 La1 Lb1 Lb2 Barium La1 Lb1 Lb2 Antimony La1 Lb1 (If necessary, more than one spectrum may be taken) • Caution is needed in case when the following peaks overlap. Antimony-Tin-Calcium Lead-Sulphur-Molybdenum Barium-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. ForensicSignificance • 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. CFSL Chandigarh

  17. Thanks

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