Gunshot Residue Analysis Notes - lect 20

Reminders

• Jury duty is finished; thanks to everyone who participated.

• Presentations went smoothly; well done to all.

• Labs this week: analytical and ballistics labs.

Gunshot Residue (GSR) Analysis

• Building upon the discussion of presumptive tests.

• Going beyond general color tests to more conclusive methods.

• Focusing on key information from instrumental techniques for ballistic investigations.

Inorganic vs. Organic Residues

• Currently, GSR analysis is mainly restricted to inorganic or metallic residues.

• Inorganic components:

  • Lead, barium, antimony (from the primer).

  • Copper and other elements from brass.

• Organic components:

  • Nitrocellulose and nitroglycerins (from the propellant).

• Organic residues absorb into the skin and evaporate more quickly.

• There is a lack of repeatable, consistent, and accepted methodologies for organic residues.

• Limited databases and information about the range of organic compounds.

• Research is ongoing at King's College London to improve understanding of organic residues.

Techniques for Assessing Inorganic Residues

• Common techniques:

  • X-ray fluorescence.

  • Atomic absorption spectroscopy.

  • Atomic emission spectroscopy (e.g., MPAES).

• These techniques provide elemental concentrations in bulk samples but lack information on morphology and individual particles.

• Morphology and Chemistry:

  • GSR particles have a characteristic spherical presentation.

  • Scanning Electron Microscopy (SEM) provides high-resolution images of individual particles.

  • Energy Dispersive X-ray analysis (EDX) is attached to SEM for chemical analysis.

  • EDX fires x-rays into the sample and measures emitted electrons to identify elements.

• SEM-EDX brings chemistry and morphology together.

Understanding GSR Composition

• Main source of inorganic content is the primer.

• Explosive compounds in primers:

  • Lead styphnate (common).

  • Lead azide (rimfire).

• Other components with specific functions.

• Mercuric Priming Mixtures:

  • Mercury fulminate (used in the past).

  • Mercury is a health and safety concern.

  • Mostly phased out, but still present in older ammunition (e.g., AK-47 ammunition).

• Synoxid Formulation:

  • Common formulation with lead styphnate as the main explosive.

  • Barium nitrate and antimony sulfide are also present.

• Additional binders, sensitizers, and frictionators may be added.

• Syntox Ammunition:

  • Greener, lead-free primer.

  • More organic-based.

  • Requires better organic analysis techniques.

Functions of Primer Components

• Lead styphnate (or similar explosive):

  • Acts as the explosive to drive the ignition process.

• Barium nitrate:

  • Acts as an oxidizer to increase the heat of ignition.

  • Ensures effective burning of the propellant.

• Antimony sulfide:

  • Acts as fuel to drive the ignition process.

  • Also acts as a frictionator, increasing friction when crushed by the firing pin.

• The goal is to have a sensitive, repeatable, and consistent detonation process.

SEM-EDX Technique Details

• SEM-EDX is widely accepted as the optimum technique for GSR analysis.

• It is well peer-reviewed and accepted in the courtroom system.

• Advantages:

  • Non-destructive (samples can be run multiple times).

  • Minimal sample prep (stubs are placed directly into the sample holder).

  • Analysis of individual particles (morphology and chemistry).

  • High confidence in identification based on elemental composition and morphology.

  • Automated process for consistency.

SEM-EDX Process

• Electron Gun:

  • A metal filament (e.g., tungsten) emits electrons when a high voltage is applied.

• Focusing Magnets:

  • Electromagnets focus the negatively charged electrons towards the target.

• Scanning Coils:

  • Change the direction of the electron beam to scan the sample surface.

• Interaction with the Sample:

  • High-energy electron beam causes excitation within the sample's chemistry.

  • Electrons are elevated in energy levels and release x-rays as they return to normal.

  • Reflected electrons are detected to reconstruct an image.

• X-rays provide chemistry.

• Reflected electrons reconstruct an image.

• Modes:

  • Manual or automated.

  • Automated is preferred for consistency.

Automated Search Parameters

• Minimum particle size to be detected.

• The system visualizes using backscattered electrons.

• Bright spots indicate denser materials.

• The system conducts further analysis when a bright spot is recognized.

• Parameters set for automated search ensure consistent data capture.

Practical Considerations

• Manual analysis is prone to personal error.

• Automated systems improve consistency but require proper setup and understanding.

• Time limitations:

  • Manual analysis of a 25 mm stub could take days.

  • Automated analysis can take around 6-8 hours per stub.

• Software Classifies Composition:

  • Provides coordinates of every particle for further manual inspection.

Data Output Examples

• Image of a particle (not always perfectly spherical).

• Different brightness indicates different chemistry across the particle.

• EDX spectrum identifies elements based on energy transitions.

• Lead (Pb) transition, barium (Ba), and aluminum (Al) are identified.

• The software can measure the size of the particles.

• The number of points measured over the particle can be set.

Particle Classification

• Classifying particles based on how representative and conclusive they are for GSR.

• Three Main Classifications:

  • Characteristic of GSR: Composition rarely found in particles from any other source. Specific to primers; not global.

  • Consistent with GSR: Compositions also found in particles from common non-firearm sources.

  • Commonly Associated with GSR: Compositions commonly found in environmental particles from numerous sources.

• A mixture of all three classifications in the same sample is strongly indicative of GSR.

  • Court Case example: Data contained all three types of GSR particles.

    • Defense attempted to use alternative explanations for each type but they did not fit holistically

    • Therefore, if sample ticks all the boxes, it is likely GSR.

  * Always think about balance of probabilties.

Example Output Data

• Software finds individual particles and provides dimensions and chemistry.

• Elemental composition:

  • Example: 34.2% barium, 29.4% oxygen, 11.8% lead, 10.8% antimony.

• Lead, barium, and antimony (the "holy trinity" for Synoxid-based primers) indicate a characteristic particle.

• Software can classify particles based on the chosen characterization system.

• Output includes all particles with their tiers (characteristic, consistent with).

• This analysis helps understand the population of particles and their origins.

False Positives for GSR

• Airbags, fireworks, and brake pads have been suggested as false positives.

• Most of these can be distinguished by morphology and/or composition.

• Considering the overall population of particles is crucial.

Car Airbags

• Airbags incorporate a primer to initiate gas production.

• The process is similar to ammunition: primers initiate chemical reactions to produce large amounts of gas.

• Impact sensors trigger the electrical impulse to the primer.

Car Brake Pads

• Older brake pads can contain lead, antimony, and barium (less common in modern times).

• Garages are a good place for false positives.

• Friction between brake pads and discs generates heat and particles that resemble GSR.

Fireworks and Pyrotechnics

• Funkier fireworks may contain various elements. Crackling balls often produce residues that contain all three main elements, particularly the bright sparkly effects; magnesium.

• Magnesium is rarely found in ammunition.

• Fireworks and pyrotechnics produce high temperatures and pressures, creating particles.

• These do not always create particularly smooth, sperical particles.

• When leaving concerts you may be covered in potential GSR like particles.

Reminders

• Jury duty is finished; thanks to everyone who participated.

• Presentations went smoothly; well done to all.

• Labs this week: analytical and ballistics labs.

Gunshot Residue (GSR) Analysis

• Building upon the discussion of presumptive tests. More in-depth examination of techniques used to identify gunshot residue.

• Going beyond general color tests to more conclusive methods. Advances in analytical methods for forensic ballistic investigations.

• Focusing on key information from instrumental techniques for ballistic investigations. Interpretation of data from instrumental techniques in ballistic contexts.

Inorganic vs. Organic Residues

• Currently, GSR analysis is mainly restricted to inorganic or metallic residues. Details on the limitations and focus of current GSR analysis.

• Inorganic components:

  • Lead, barium, antimony (from the primer). Key elements from the primer, facilitating GSR identification.

  • Copper and other elements from brass. Minor but detectable elements originating from cartridge casings.

• Organic components:

  • Nitrocellulose and nitroglycerins (from the propellant). Key organic compounds derived from the propellant.

• Organic residues absorb into the skin and evaporate more quickly. Challenges in detecting organic residues due to their transient nature.

• There is a lack of repeatable, consistent, and accepted methodologies for organic residues. Issues in standardization for organic GSR analysis.

• Limited databases and information about the range of organic compounds. Gaps in knowledge regarding comprehensive organic compound profiling.

• Research is ongoing at King's College London to improve understanding of organic residues. Efforts to address gaps in organic residue analysis.

Techniques for Assessing Inorganic Residues

• Common techniques:

  • X-ray fluorescence. A non-destructive technique used to determine the elemental composition of materials.

  • Atomic absorption spectroscopy. A technique used to measure the concentration of elements in a sample by measuring the absorption of light.

  • Atomic emission spectroscopy (e.g., MPAES). A technique that analyzes the light emitted by excited atoms to determine elemental composition.

• These techniques provide elemental concentrations in bulk samples but lack information on morphology and individual particles. Limitations of bulk analysis techniques in GSR analysis.

• Morphology and Chemistry:

  • GSR particles have a characteristic spherical presentation. The distinctive shape of GSR particles aiding identification.

  • Scanning Electron Microscopy (SEM) provides high-resolution images of individual particles. Detailed surface imaging technique for particle analysis.

  • Energy Dispersive X-ray analysis (EDX) is attached to SEM for chemical analysis. Technique for elemental analysis combined with SEM imaging.

  • EDX fires x-rays into the sample and measures emitted electrons to identify elements. Process by which EDX identifies the elemental composition of particles.

• SEM-EDX brings chemistry and morphology together. Advantages of combined SEM-EDX in GSR analysis.

Understanding GSR Composition

• Main source of inorganic content is the primer. Origin of key inorganic elements found in GSR.

• Explosive compounds in primers:

  • Lead styphnate (common). A common initiating explosive found in primers.

  • Lead azide (rimfire). Another explosive compound specific to rimfire ammunition.

• Other components with specific functions. Role of additional components in primers to ensure reliable ignition.

• Mercuric Priming Mixtures:

  • Mercury fulminate (used in the past). An outdated initiating explosive containing mercury.

  • Mercury is a health and safety concern. Health concerns leading to the decline in mercury-based primers.

  • Mostly phased out, but still present in older ammunition (e.g., AK-47 ammunition). Persistence of mercury-based primers in certain ammunition types.

• Synoxid Formulation:

  • Common formulation with lead styphnate as the main explosive. Details on the composition of Synoxid primers.

  • Barium nitrate and antimony sulfide are also present. Additional components found in Synoxid primers augmenting explosive properties.

• Additional binders, sensitizers, and frictionators may be added. Enhancing primer performance through specialized additives.

• Syntox Ammunition:

  • Greener, lead-free primer. An environmentally friendlier alternative using organic compounds.

  • More organic-based. Increased reliance on organic compounds in lead-free primers.

  • Requires better organic analysis techniques. The necessity of improved methods when using lead-free primers.

Functions of Primer Components

• Lead styphnate (or similar explosive):

  • Acts as the explosive to drive the ignition process. Initiating the burning of propellant.

• Barium nitrate:

  • Acts as an oxidizer to increase the heat of ignition. Boosting heat output to ensure consistent propellant combustion.

  • Ensures effective burning of the propellant. Supporting complete burning of the propellant.

• Antimony sulfide:

  • Acts as fuel to drive the ignition process. Fueling combustion to maintain reliable ignition.

  • Also acts as a frictionator, increasing friction when crushed by the firing pin. Enhancing sensitivity and reliability by creating friction upon impact.

• The goal is to have a sensitive, repeatable, and consistent detonation process. Ensuring reliable and predictable primer ignition every time.

SEM-EDX Technique Details

• SEM-EDX is widely accepted as the optimum technique for GSR analysis. Reliability and wide acceptance of SEM-EDX in forensic analysis.

• It is well peer-reviewed and accepted in the courtroom system. Validated analysis method with backing from scientific community and legal acceptance.

• Advantages:

  • Non-destructive (samples can be run multiple times). Preservation of samples allowing for repeat testing.

  • Minimal sample prep (stubs are placed directly into the sample holder). Efficient analysis using direct mounting.

  • Analysis of individual particles (morphology and chemistry). Comprehensive assessment through combined features.

  • High confidence in identification based on elemental composition and morphology. Precise identification of GSR particles.

  • Automated process for consistency. Consistent results with minimized manual error via automation.

SEM-EDX Process

• Electron Gun:

  • A metal filament (e.g., tungsten) emits electrons when a high voltage is applied. Production of electron beam through high voltage application in SEM-EDX.

• Focusing Magnets:

  • Electromagnets focus the negatively charged electrons towards the target. Ensuring beam targeting accuracy by magnetic lens focusing.

• Scanning Coils:

  • Change the direction of the electron beam to scan the sample surface. Scanning the electron beam to cover the entire sample surface ensuring thorough analysis.

• Interaction with the Sample:

  • High-energy electron beam causes excitation within the sample's chemistry. Sample excitation through high-energy electron interaction.

  • Electrons are elevated in energy levels and release x-rays as they return to normal. Emission of X-rays as excited electrons return to stable state.

  • Reflected electrons are detected to reconstruct an image. Image construction via detection of reflected electrons.

• X-rays provide chemistry. Elemental analysis by X-ray detection during SEM-EDX.

• Reflected electrons reconstruct an image. Surface morphology by detecting reflected electrons.

• Modes:

  • Manual or automated. Flexible operation of SEM-EDX in manual and automated setups.

  • Automated is preferred for consistency. Optimization for consistency by using automated analysis.

Automated Search Parameters

• Minimum particle size to be detected. Setting detection thresholds based on size.

• The system visualizes using backscattered electrons. Visualization of denser materials via backscattered electron imaging.

• Bright spots indicate denser materials. Identification of areas of interest using density contrast.

• The system conducts further analysis when a bright spot is recognized. Automated in-depth analysis of potential GSR particles.

• Parameters set for automated search ensure consistent data capture. Achieving uniformity in data acquisition with defined parameters.

Practical Considerations

• Manual analysis is prone to personal error. Potential for errors in manual analysis.

• Automated systems improve consistency but require proper setup and understanding. Correct configuration and expertise necessary for automated analysis.

• Time limitations:

  • Manual analysis of a 25 mm stub could take days. Long duration of manual GSR analysis.

  • Automated analysis can take around 6-8 hours per stub. Significantly reduced turnaround using automated techniques.

• Software Classifies Composition:

  • Provides coordinates of every particle for further manual inspection. Coordinates for each partile for further inspection

Data Output Examples

• Image of a particle (not always perfectly spherical). Visual representation of detected particles.

• Different brightness indicates different chemistry across the particle. Mapping elemental distribution within particles.

• EDX spectrum identifies elements based on energy transitions. Defining the chemical composition with EDX spectra.

• Lead (Pb) transition, barium (Ba), and aluminum (Al) are identified. Tracing elemental signatures for conclusive identifications.

• The software can measure the size of the particles. Measuring each particles size.

• The number of points measured over the particle can be set. Setting measuring values for elements.

Particle Classification

• Classifying particles based on how representative and conclusive they are for GSR. Categorizing particles based on GSR characteristics.

• Three Main Classifications:

  • Characteristic of GSR: Composition rarely found in particles from any other source. Specific to primers; not global. Particle types with virtually unique GSR signatures crucial in positive identifications.

  • Consistent with GSR: Compositions also found in particles from common non-firearm sources. Particle types indicating likely GSR but shared with other environmental contaminants.

  • Commonly Associated with GSR: Compositions commonly found in environmental particles from numerous sources. Environmental particles which don't conclusively indicate GSR.

• A mixture of all three classifications in the same sample is strongly indicative of GSR.

  • Court Case example: Data contained all three types of GSR particles.

    • Defense attempted to use alternative explanations for each type but they did not fit holistically

    • Therefore, if sample ticks all the boxes, it is likely GSR.

  * Always think about balance of probabilties.

Example Output Data

• Software finds individual particles and provides dimensions and chemistry. Automated detection of particles accompanied by dimensional and elemental information.

• Elemental composition:

  • Example: 34.2% barium, 29.4% oxygen, 11.8% lead, 10.8% antimony.

• Lead, barium, and antimony (the "holy trinity" for Synoxid-based primers) indicate a characteristic particle. The diagnostic trio for traditional primer composition, enabling strong GSR assertion.

• Software can classify particles based on the chosen characterization system. Data sorting based on established categorization schemes for GSR analysis.

• Output includes all particles with their tiers (characteristic, consistent with). Comprehensive results displaying particle attributes and associated categories.

• This analysis helps understand the population of particles and their origins. Providing insights into distributions, source assessment of GSR particles.

False Positives for GSR

• Airbags, fireworks, and brake pads have been suggested as false positives. Potential sources of common interference, stressing caution in analysis.

• Most of these can be distinguished by morphology and/or composition. Differentiation based on distinct physical and chemical traits.

• Considering the overall population of particles is crucial. Understanding context-specific populations for correct interpretation.

Car Airbags

• Airbags incorporate a primer to initiate gas production. Airbag deployment mechanism relies on primer-induced gas release.

• The process is similar to ammunition: primers initiate chemical reactions to produce large amounts of gas. Functional similarities of primers in airbag and ammunition mechanics.

• Impact sensors trigger the electrical impulse to the primer. Deployment triggered through impact detection, resulting in airbag actuation.

Car Brake Pads

• Older brake pads can contain lead, antimony, and barium (less common in modern times). Chemical similarities to GSR in aging brake systems pose identification challenges.

• Garages are a good place for false positives. Locations associated with brake maintenance increasing GSR-like particle incidence.

• Friction between brake pads and discs generates heat and particles that resemble GSR. Particle formation due to frictional heating in brake systems.

Fireworks and Pyrotechnics

• Funkier fireworks may contain various elements. Crackling balls often produce residues that contain all three main elements, particularly the bright sparkly effects; magnesium.

• Magnesium is rarely found in ammunition. A distinguishing feature, with presence tipping towards pyrotechnic origins.

• Fireworks and pyrotechnics produce high temperatures and pressures, creating particles. Conditions favoring particle generation mimicking firearm discharge.

• These do not always create particularly smooth, sperical particles. Morphological variations allowing distinction from GSR.

• When leaving concerts you may be covered in potential GSR like particles.