Gunshot Residue (GSR) In-Depth Notes

GSR refers to the tiny particles expelled when a firearm is discharged. These residues originate from the primer particles in ammunition and can provide crucial evidence in forensic investigations. GSR commonly contains elements like Lead (Pb), Barium (Ba), and Antimony (Sb), which can be significant indicators of firearm involvement. The presence of GSR in an individual’s vicinity, especially on their clothing or skin, can suggest recent handling or discharge of a firearm.

Collection Methods

  • GSR Collection Sites:

    • Hands: This site is the most common for collection because it is directly exposed during firearm discharges.

    • Hair, Face, Clothing, and Large Objects: These serve as secondary sites where residue may also collect, demonstrating the potential for cross-contamination.

  • GSR Kit: Specialized kits designed for the collection of GSR are used to ensure findings are preserved as evidence. For instance, Canadian GSR kits include bilingual forms approved by the Royal Canadian Mounted Police (RCMP) to facilitate standard operating procedures across bilingual populations.

GSR Composition

  • Characteristic Composition: The elemental composition typically includes Pb/Ba/Sb, which when analyzed can confirm the presence of GSR. However, variations such as Sb/Ba and Pb/Sb may also indicate residue presence, emphasizing the need for thorough analysis.

Analysis Techniques

  • Current Methods: Modern forensic analysis often employs scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) to identify inorganic components of GSR accurately. These techniques provide detailed information regarding the composition of the particles.

  • Limitations exist, however, as these methods focus solely on inorganic compounds; consequently, there is a necessity for further exploration of organic residues possibly present, which may indicate different sources of contamination or shooting activity.

Interpretation of GSR Evidence
Hierarchy of Proposition for GSR Evidence

  1. Offence Level (III): Did the Person of Interest (POI) shoot the victim?

    • Hypothesis (Hp): The POI murdered the victim.

    • Hypothesis (Hd): An unknown person murdered the victim.

  2. Activity Level (II): Did the POI discharge a firearm?

    • Hypothesis (Hp): The POI discharged a firearm or a related combination of actions.

    • Hypothesis (Hd): An unknown person discharged a firearm.

  3. Source Level (I): Is the residue from the POI's hands GSR?

    • Hypothesis (Hp): Trace is from a discharged firearm (is GSR).

    • Hypothesis (Hd): The trace is from an environmental source (is not GSR).

Interpretation Challenges

  • Assessing the source of GSR remains a challenge due to potential contamination from non-firearm sources, such as brake pads, fireworks, or industrial chemicals that may share similar elemental signatures.

  • Significant factors affecting interpretation include GSR transfer methods, the persistence of residue, and the potential for contamination through physical contact with surfaces that may have come into contact with firearms.

GSR Transfer Methods

  • Primary Transfer: This occurs when GSR is directly deposited onto surfaces in proximity during the act of discharging a firearm.

  • Secondary Transfer: GSR is transferred from contaminated surfaces to clean surfaces, such as through handshake or handling contaminated objects.

    • Examples of Secondary Transfer:

    • Direct contact with the shooter immediately after discharge.

    • Handling firearms known to be contaminated with GSR.

    • Cross-contamination between clothing items if individuals are in close proximity while handling firearms.

GSR Persistence

  • GSR is known to be rapidly lost after exposure to environmental conditions and time. The expected decline in traces of GSR is significant, particularly within the first few hours post-discharge.

  • Therefore, collection is critical within 6 to 12 hours after firearm discharge to achieve the most accurate and reliable results.

Factors Impacting GSR Collection

  • Fabric Type: The efficiency of collecting residues can vary widely depending on fabric types such as cotton, leather, or synthetic fibers, each interacting differently with GSR particles.

  • Shooting Distance: The distance from which the firearm is discharged influences both the quantity and distribution of GSR particles gathered on surfaces and individuals nearby.

Legal Cases Involving GSR

  • Case Studies:

    • R. v. Glasgow: This case identified significant GSR particles, indicating potential firearm discharge exposure, which proved crucial for establishing an evidentiary link.

    • R. v. Woodcock: This case highlighted that while the presence of GSR can indicate proximity to firearms, it is not conclusive evidence of actual discharge, necessitating further corroborative evidence.

    • R. v. Admasu: This case emphasized the uncertainty regarding the sources of GSR when there wasn't clear evidence confirming discharge, showcasing the complications in interpreting GSR findings in various contexts.

Organic GSR (OGSR)

  • Emergence: The introduction of organic GSR with new ammunition types aims to minimize the environmental and health impacts associated with traditional GSR, such as reducing heavy metals and toxic material release.

  • Collection Complexity: Analyzing OGSR can be more involved, potentially requiring gas chromatography and mass spectrometry to ensure a thorough assessment of residues present.

  • Concentration Trends: GSR concentration decreases notably, with approximately 80% loss reported after 2 hours, underscoring the need for rapid collection to ensure accurate forensic analysis.

Significant Findings

  • Typical GSR counts observed can range from 0 to 3000 particles following discharge of a firearm.

  • GSR can travel considerable distances upon discharge, with particles able to cover up to 60 ft forwards, laterally, or backwards from the firearm discharge point, indicating the potential reach of contamination following a shooting incident.