Gunshot Residue Analysis Notes - lect 19

General Reminders

• Jury duties and labs for some on Wednesday and Friday this week.

• Presentations on Thursday (morning or afternoon sessions).

  • Upload PowerPoint files to Moodle by lunchtime tomorrow (PowerPoint files, not PDFs).

  • Presentations as per briefs.

  • One question from instructor, one minute to confer, then answer.

  • Peer marking (bring an electronic device).

• Intense day; be on time.

Gunshot Residue Analysis

• Second to last topic of the term.

Aims

• Understand GSR creation, composition, and morphology.

• Appreciate potential contamination issues (extremely important).

• Understand analysis via scanning electron microscopy (SEM).

• Understand standard GSR classifications.

• Differentiate between samples and how it relates to the court system.

Definition of Gunshot Residue (GSR)

• Any particles or residues discharged from a firearm after the trigger is pulled.

• Includes chemicals from the primer, propellant, oxidizers, reducing agents, sensitizers, and binders.

• Also includes residues from the weapon itself and cartridge case.

Alternative Terms for GSR

• Firearm Discharge Residue (FDR) - common in European systems

• Cartridge Discharge Residue

• Gunfire Residue

• Primer Discharge Residue

All essentially mean the same thing.

Sources of Chemical Residues

• Explosive reaction of the primer.

• Material from the bullet and bullet jacket.

  • Bullet core (lead-antimony alloy).

    • Note: Lead and antimony may also come from the primer.

• Material eroded from the cartridge case and primer cup.

  • Cartridge case (brass - copper and other alloys).

  • Primer cup (aluminum based).

• Materials originating from the interior of firearm chamber and barrel.

  • Includes residues from previous discharges.

  • Firing different types of ammunition through the same weapon leads to a complex mixture of residues.

Formation of GSR

• High temperatures and pressures inside the firearm during activation.

• Creates a gaseous mixture that propels the bullet down the barrel.

• Gaseous mixture is expelled from the end of the barrel and any spaces in the firearm.

  • Residues also expelled from the breach area when the weapon cycles.

• Residues form due to rapid cooling of discharge gases and solid matter.

  • Hot gases hit the cooler external environment.

  • Particles cool and condense rapidly (gas to liquid to solid).

• Gases condense into spherical particles due to aerodynamic drag forces.

  • Spherical particles are indicative of GSR.

  • Morphology (shape) and chemistry are exploited for analysis.

• Some solid residues may not fully burn, forming complex mixtures and aggregate forms.

• Most residues show evidence of exposure to extremely high temperature and pressure.

Presentation of Gunshot Residue

• Spheroidal particles ranging in size from sub-micrometer to several hundred micrometers.

  • Microscopic, generally invisible to the naked eye.

• Larger particles in irregular or aggregate form.

Examples of GSR Particles

• Typical spheroidal GSR particle (20-25 micrometers across).

• Irregular example (70 micrometers across).

• Aggregate particle (10-15 micrometers across).

• Unburned primer material (1 millimeter across).

• Unactivated propellant granules (1 millimeter across).

  • Spherical, rods, rods with holes, lamelle/tile shapes

Forensic Considerations

• Aim: Understand the chemistry of a weapon or suggest if a weapon was fired in a scene.

• GSR is like dust and can be easily transferred between scenes.

• Finding GSR doesn't necessarily mean someone fired a weapon there.

• Interpretation of GSR evidence must be done with care.

Avoiding Contamination

• Taking appropriate steps at all stages.

• Firearms officers entering a shooting scene contaminate it with their own GSR.

• Medical care comes before forensic considerations.

• Full PPE required when collecting samples.

• GSR gets everywhere, sticks to surfaces, and doesn't degrade easily (mostly inorganic).

Sampling and Collection

• Collect samples from a suspect or victim.

• Sample the subject prior to any handcuffing.

• Primary sampling area is the hands (back and front).

• Use specialist stubs (sticky stubs) to collect GSR.

• Forensic kits are sealed and remain unopened until use.

• Effectiveness is time-dependent.

  • High likelihood of finding GSR if sampled soon after the shooting.

  • Hand washing removes most particles.

  • Avoid hand washing before sampling.

• Internal swabs can be taken (autopsy).

  • Contain biological material, so chill samples quickly.

• Organic components of GSR can be absorbed into the body.

• Evaporative loss through sweat.

• Secondary transfer by touching other objects.

Human Sampling

• Use SEM (scanning electron microscope) stubs.

  • Aluminum disc with a carbon sticky (double-sided carbon tape).

  • Dab the sticky stub over the back and front of individual's hands in a line pattern.

  • Seal container, put in evidence bags, and send for laboratory analysis.

Anti-Contamination Procedures

• A lot of anti contamination procedures used to maintain chain of custody.

Live Firearm Found

• Don't mess around with the gun.

• If live firearm is found the best thing to do to make it safe is get a firearms officer.

Famous Case: Barry George

• Accused of murdering Jill Dando.

• Convicted based on one or two GSR particles in his pocket.

• Conviction overturned because that level of contamination can easily be found elsewhere.

Range of Gunshot Residue

• Particles cool quickly and don't travel significant distances like bullets.

• Clear GSR pattern visible at an arm's length.

• Residues can travel several meters, depending on the firearm system and ammunition.

• Residue pattern can help understand what happened at the scene.

Chemical Tests

• Chemical dyes can stain GSR for pattern analysis.

• Chemical analysis should happen before staining, so no chemical modification has been done to the wanted samples.

• Residues also present on bullets.

Discharge Patterns

• Gunshot residue pattern from testing the suspect weapon and ammunition can provide insight into the range of the suspect weapon.

Chemical Tests for GSR

• Two main tests can visualize and indicate GSR presence.
  If both are positive, it is strongly suggestive that it is GSR.

Greiss Test

• Presumptive test for organic nitrite compounds.

• Reagents:

  • 0.2\% {solution of naphthalene diamine dihydrochloride}

  • 2\% {sulfonylamide in } 5\% {phosphoric acid}

• Spray onto the surface; brownish-orange color indicates organic nitrates.

• Organic nitrates can come from multiple sources.

• Historically used as a confirmatory test.

  • Case example is the Birmingham Six.

    • Individuals were falsely convicted based on grease test as they did the test positive.

    • Residues were later shown to be found on a variety of objects, even coated playing cards were give a positive result.

Sodium Rhodizonate Test

• Presumptive test for lead.

  • Lead originates from: bullets (lead antimony alloy) and primers (lead stiffnate or lead azide).

• Solution: 1% solution of sodium rhodizonate in distilled water.

• Spray on the sample, a red or pink color indicates lead.

• Treat with dilute hydrochloric acid, the stain turns blue.

• Confirmatory series of reactions strongly suggests lead is present.

Less likely to have lead and organic nitrates in the same place at the same time unless it's GSR from a firearm.

General Reminders

• Jury duties and labs for some on Wednesday and Friday this week.

• Presentations on Thursday (morning or afternoon sessions).

  • Upload PowerPoint files to Moodle by lunchtime tomorrow (PowerPoint files, not PDFs).

  • Presentations as per briefs.

  • One question from instructor, one minute to confer, then answer.

  • Peer marking (bring an electronic device).

• Intense day; be on time.

Gunshot Residue Analysis

• Second to last topic of the term.

Aims

• Understand GSR creation, composition, and morphology.

• Appreciate potential contamination issues (extremely important).

• Understand analysis via scanning electron microscopy (SEM).

• Understand standard GSR classifications.

• Differentiate between samples and how it relates to the court system.

Definition of Gunshot Residue (GSR)

• Any particles or residues discharged from a firearm after the trigger is pulled.

• Includes chemicals from the primer, propellant, oxidizers, reducing agents, sensitizers, and binders.

• Also includes residues from the weapon itself and cartridge case.

Alternative Terms for GSR

• Firearm Discharge Residue (FDR) - common in European systems

• Cartridge Discharge Residue

• Gunfire Residue

• Primer Discharge Residue

All essentially mean the same thing.

Sources of Chemical Residues

• Explosive reaction of the primer.

• Material from the bullet and bullet jacket.

  • Bullet core (lead-antimony alloy).

  • Note: Lead and antimony may also come from the primer.

• Material eroded from the cartridge case and primer cup.

  • Cartridge case (brass - copper and other alloys).

  • Primer cup (aluminum based).

• Materials originating from the interior of firearm chamber and barrel.

  • Includes residues from previous discharges.

  • Firing different types of ammunition through the same weapon leads to a complex mixture of residues. This can complicate analysis, requiring careful differentiation between different types of GSR.

Formation of GSR

• High temperatures and pressures inside the firearm during activation. Typical pressures can reach several thousand PSI, and temperatures can exceed 2000^\circ C.

• Creates a gaseous mixture that propels the bullet down the barrel.

• Gaseous mixture is expelled from the end of the barrel and any spaces in the firearm.

  • Residues also expelled from the breach area when the weapon cycles. The amount and location of GSR expelled from the breach can vary depending on the firearm's design and condition.

• Residues form due to rapid cooling of discharge gases and solid matter.

  • Hot gases hit the cooler external environment.

  • Particles cool and condense rapidly (gas to liquid to solid). This rapid phase transition is critical to the formation of the characteristic spherical GSR particles.

• Gases condense into spherical particles due to aerodynamic drag forces.

  • Spherical particles are indicative of GSR. However, not all spherical particles are GSR, so chemical analysis is essential.

  • Morphology (shape) and chemistry are exploited for analysis.

• Some solid residues may not fully burn, forming complex mixtures and aggregate forms. These can include partially burned propellant and primer fragments.

• Most residues show evidence of exposure to extremely high temperature and pressure. This can lead to the formation of unique compounds and elemental compositions.

Presentation of Gunshot Residue

• Spheroidal particles ranging in size from sub-micrometer to several hundred micrometers.

  • Microscopic, generally invisible to the naked eye. Advanced imaging techniques are required for their detection and analysis.

• Larger particles in irregular or aggregate form. These may be more visible but less indicative of GSR due to their non-specific morphology.

Examples of GSR Particles

• Typical spheroidal GSR particle (20-25 micrometers across). These particles are often the primary target of GSR analysis.

• Irregular example (70 micrometers across). These particles may require further analysis to confirm their origin.

• Aggregate particle (10-15 micrometers across). These are clusters of smaller particles and can be more challenging to analyze.

• Unburned primer material (1 millimeter across).

• Unactivated propellant granules (1 millimeter across).

  • Spherical, rods, rods with holes, lamelle/tile shapes. These shapes are characteristic of different types of propellants.

Forensic Considerations

• Aim: Understand the chemistry of a weapon or suggest if a weapon was fired in a scene. This can help reconstruct events and link suspects to firearms.

• GSR is like dust and can be easily transferred between scenes. This makes contamination a significant concern.

• Finding GSR doesn't necessarily mean someone fired a weapon there. It could be transferred from another location or source.

• Interpretation of GSR evidence must be done with care. Requires consideration of potential sources of contamination and transfer.

Avoiding Contamination

• Taking appropriate steps at all stages. This includes using proper PPE, cleaning equipment, and avoiding cross-contamination between samples.

• Firearms officers entering a shooting scene contaminate it with their own GSR. They should take precautions to avoid transferring GSR to the scene.

• Medical care comes before forensic considerations. However, medical personnel should also be aware of the potential for contamination and take steps to minimize it.

• Full PPE required when collecting samples. This includes gloves, masks, and protective clothing.

• GSR gets everywhere, sticks to surfaces, and doesn't degrade easily (mostly inorganic). This persistence makes it both a valuable forensic marker and a contamination risk.

Sampling and Collection

• Collect samples from a suspect or victim. Samples should be collected as soon as possible after the event.

• Sample the subject prior to any handcuffing. Handcuffing can transfer GSR from the hands to the cuffs, potentially contaminating other surfaces.

• Primary sampling area is the hands (back and front). These are the areas most likely to come into contact with GSR.

• Use specialist stubs (sticky stubs) to collect GSR. These stubs are designed to efficiently collect particles from surfaces.

• Forensic kits are sealed and remain unopened until use. This ensures that the collection materials are free from contamination.

• Effectiveness is time-dependent.

  • High likelihood of finding GSR if sampled soon after the shooting. The longer the delay, the greater the chance that GSR will be lost or transferred.

  • Hand washing removes most particles. This is why it is important to collect samples before suspects wash their hands.

  • Avoid hand washing before sampling.

• Internal swabs can be taken (autopsy).

  • Contain biological material, so chill samples quickly. This prevents degradation of the biological material and preserves the integrity of the sample.

• Organic components of GSR can be absorbed into the body. This can complicate analysis, as the GSR may be present in trace amounts.

• Evaporative loss through sweat. Sweat can wash away GSR particles from the skin.

• Secondary transfer by touching other objects. This can lead to the spread of GSR to other locations and surfaces.

Human Sampling

• Use SEM (scanning electron microscope) stubs.

  • Aluminum disc with a carbon sticky (double-sided carbon tape). The carbon tape provides an adhesive surface for collecting GSR particles.

  • Dab the sticky stub over the back and front of individual's hands in a line pattern. This ensures thorough coverage of the hands.

  • Seal container, put in evidence bags, and send for laboratory analysis. Proper sealing and labeling are essential for maintaining chain of custody.

Anti-Contamination Procedures

• A lot of anti contamination procedures used to maintain chain of custody. These procedures are designed to prevent contamination of samples and ensure the integrity of the evidence.

Live Firearm Found

• Don't mess around with the gun. Handling the firearm can alter evidence and create a safety hazard.

• If live firearm is found the best thing to do to make it safe is get a firearms officer. Firearms officers are trained to safely handle and secure firearms.

Famous Case: Barry George

• Accused of murdering Jill Dando.

• Convicted based on one or two GSR particles in his pocket.

• Conviction overturned because that level of contamination can easily be found elsewhere. This case highlights the importance of considering potential sources of contamination when interpreting GSR evidence.

Range of Gunshot Residue

• Particles cool quickly and don't travel significant distances like bullets. This limits the spread of GSR and makes it a useful indicator of proximity to a firearm.

• Clear GSR pattern visible at an arm's length. This is the typical range for detecting GSR on a shooter's hands.

• Residues can travel several meters, depending on the firearm system and ammunition. Factors such as barrel length, ammunition type, and environmental conditions can affect the range.

• Residue pattern can help understand what happened at the scene. The distribution of GSR can provide clues about the position of the shooter and the victim.

Chemical Tests

• Chemical dyes can stain GSR for pattern analysis. This can help visualize the distribution of GSR on a surface.

• Chemical analysis should happen before staining, so no chemical modification has been done to the wanted samples. Staining can interfere with subsequent chemical analysis.

• Residues also present on bullets. Analysis of GSR on bullets can provide information about the type of ammunition used.

Discharge Patterns

• Gunshot residue pattern from testing the suspect weapon and ammunition can provide insight into the range of the suspect weapon. This can help determine whether a particular firearm was used in a shooting.

Chemical Tests for GSR

• Two main tests can visualize and indicate GSR presence.

  • If both are positive, it is strongly suggestive that it is GSR. However, confirmatory analysis is still required.

Greiss Test

• Presumptive test for organic nitrite compounds.

• Reagents:

  • 0.2\% {solution of naphthalene diamine dihydrochloride}

  • 2\% {sulfonylamide in } 5\% {phosphoric acid}

• Spray onto the surface; brownish-orange color indicates organic nitrates. The intensity of the color can provide a rough estimate of the amount of organic nitrates present.

• Organic nitrates can come from multiple sources. This limits the specificity of the Greiss test.

• Historically used as a confirmatory test.

  • Case example is the Birmingham Six.

    • Individuals were falsely convicted based on grease test as they did the test positive.

    • Residues were later shown to be found on a variety of objects, even coated playing cards were give a positive result. This case highlights the limitations of presumptive tests and the importance of confirmatory analysis.

Sodium Rhodizonate Test

• Presumptive test for lead.

  • Lead originates from: bullets (lead antimony alloy) and primers (lead stiffnate or lead azide).

• Solution: 1% solution of sodium rhodizonate in distilled water.

• Spray on the sample, a red or pink color indicates lead. The intensity of the color can provide a rough estimate of the amount of lead present.

• Treat with dilute hydrochloric acid, the stain turns blue. This color change is a characteristic reaction of lead with sodium rhodizonate.

• Confirmatory series of reactions strongly suggests lead is present. This helps to rule out false positives.

Less likely to have lead and organic nitrates in the same place at the same time unless it's GSR from a firearm. However, it is still important to perform confirmatory analysis to rule out other possible sources.