Gunshot Residue Particle Analysis Technique

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

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)

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

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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

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

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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

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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

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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

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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

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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 gt 1/10 but lt1/3 highest peak
• Trace peak 1/10 highest peak or less, but still
  clearly identifiable

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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)

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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.

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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.

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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

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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.

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Thanks