Topic 10 - Gunshot Residue Analysis Flashcards
What is gunshot residue?
Particles, primer, agents
“Any particles or residues discharged from a firearm after the trigger has been pulled. These may include chemicals from the primer, propellant, oxidisers, reducing agents, sensitisers and binders.”
What are the sources of GSR?
Bullet, cartridge, chamber, barrel
- Residues formed through the explosive reaction of the primer compounds.
- Material originating from the bullet and bullet jacket or coating.
- Material eroded from the cartridge case, primer cup and other cartridge components.
- Materials originating from the interior of the firearm chamber and barrel, including residues from previous discharges of the firearm and foreign materials, such as metal oxidation/corrosion, soil, and debris, including
biological material.
How is GSR formed?
Rapid cooling
- Rapid cooling of the discharge gases and solid matter, originating from partially reacted components of the primer and propellant, as well as from the metallic components of the ammunition and firearm.
What happens to the gases in terms of GSR?
Condense
- Some of the gases condense to spheres and also interact with solid residue materials to form complex mixtures and aggregate forms.
- Some residue material can be ejected with little or no physical or chemical modification, but most residue particles show evidence of exposure to or formation at extremely high temperatures and pressure.
What is the general appearance of GSR?
Aggregate
- Spheroidal particles ranging in size from sub-micrometres (μm) to several hundred micrometres in diameter.
- Irregular and aggregate particles, which generally constitute the majority of larger GSR particles produced, ranging in size from a few micrometres to several hundred micrometres.
When taking GSR samples from a suspect what should you try ensure?
- Sample from the subject prior to handcuffing.
- Subject should be under visual observation before sample collection.
- Do not allow subject to wash/wipe hands.
- Do not allow subject to use the bathroom before collection. If the urge is irresistible and unavoidable, the subject should be supervised to
ensure that he does not wash his hands. - Do not allow subject to place hands in pockets.
- Do not remove subject’s clothing before GSR sample collection.
- Do not fingerprint the subject before GSR collection.
Where should biological samples be stored?
Degrading
All biological GSR samples to be refrigerated immediately to prevent biological action degrading any nitrate compounds.
What additional GSR samples can be taken with permission?
- Medical practitioners can swab nasal passages with the subject’s permission.
- There is no power in law to take this type of sample by force.
What can pathologists swab post-mortem? GSR
Pathologists can swab sinuses and recover mucous post-mortem.
Where are the hand-sampling areas? (GSR)
- The back of each hand including the thumb-forefinger web as well as all digits
- The palm of each hand including web of hand as well as all digits.
How should GSR sampling from a suspect’s hand be done?
- Dab the hand sampling areas in a ‘line search
pattern’ up and down the palm, fingers and webbing with an SEM stub in its holder. - Separate stubs for at least front and back of hand.
What anti-contamination procedures should be carried out for GSR?
Equipment, assessment, contamination, collection, PPE
- All equipment should be stored in a clean environment isolated from potential contamination.
- When undertaking an examination, the equipment should be protected from exposure to potential contamination.
- Carry out an initial scene assessment.
- Avoid dealing with other items or evidence that can be heavily contaminated before sampling for GSR.
- Identify a collection area that is isolated from areas that may be contaminated.
- Clean the collection area
- Wash hands and put on any PPE before sampling
- Minimise or avoid direct contact with the areas to be sampled
What anti-contamination procedures should be carried out for GSR? (2)
ASAP, deviations, clean area, integrity, gloves, monitor
- Only open one sampling container at a time.
- Take samples as soon as possible to avoid loss of possible evidence.
- Properly seal and label the sample tube to preserve the integrity and continuity of the
sample. - When the sampling has been completed remove and discard the gloves appropriately.
- Fill out the collection data sheet after the samples have been taken.
- Document any deviations from the instructions and checklist provided.
- Note any other information that could be relevant on the kit data/information sheet.
- Seal the samples and keep the data sheet separate from samples in case it has become
contaminated: consider double bagging of the evidence kits as an extra anticontamination precaution. - Store the evidence (used) kits in a clean area to avoid contaminating the surface of the packaging: isolate the kits from firearms and ammunition.
- Consider using separate lockers dedicated to GSR Kits and other items for GSR analysis.
- Monitor storage areas to show cleaning and procedures are effective.
What should you do with GSR at close range?
Dyes
- GSR on surfaces other than human tissue is best recovered by removing as large a section as possible
- The overall residue pattern can be just as important as the chemical composition of the particles.
- Dyes can be used to stain the GSR for pattern analysis.
- Any samples for chemical analysis should be taken prior to staining.
- If unsure, swab from one area then recover the remainder of the sample.
What should you do with GSR at long range?
Deposits, wipe ring
- GSR will not be present much beyond a few metres from point of shot.
- However, important residue deposits will be present on the bullet and these will deposit onto any surface it interacts with. The bullet will leave a “wipe ring” if it passes through the impacted target.
- The deposits on the bullet and in the wipe ring can be analysed.
- These may also contain contaminants collected prior to impact.
- The collection process should ideally be conducted in a laboratory: no on-scene analysis or recovery should be attempted unless it’s
unavoidable. - Instead, recover the entire sample to a laboratory if possible.
What can you do with a GSR discharge pattern?
Analysed, test pattern, conditions
- GSR discharge patterns can be analysed for any firearm and ammunition combination and will be relatively consistent at any given range.
- A test pattern can be fired using the subject firearm and ammunition and the results compared to a distribution found deposited on a scene surface.
- This method is relatively accurate as long as most conditions are replicated.
- The ammunition is key though, since different manufacturers use different propellant designs.
What is the Greiss test?
Explosive materials
- The Greiss test is a presumptive chemical test
which suggests the presence of organic nitrite
compounds. - It is used to test for traces of explosive materials and propellants and turns brown/orange in their presence.
- It is presumptive since it can give false
positive results in some circumstances.
What is the sodium rhodizonate test?
The sodium rhodizonate test is a chemical metal
deposition test which suggests the presence of lead
When is the sodium rhodizonate test performed?
It can be performed after the Greiss test and involves spraying a 1% solution of the reagent in distilled water onto the test surface.
What colours does the sodium rhodizonate test give?
- This produces a red/pink stain suggesting the presence of lead.
- The area is then treated with dilute HCl and if the stain turns blue then the presence of lead is confirmed.