Topic 10 - Gunshot Residue Analysis

Question 1

What is gunshot residue?

Particles, primer, agents

Answer 1

“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.”

Question 2

What are the sources of GSR?

Bullet, cartridge, chamber, barrel

Answer 2

• 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.

Question 3

How is GSR formed?

Rapid cooling

Answer 3

• 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.

Question 4

What happens to the gases in terms of GSR?

Condense

Answer 4

• 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.

Question 5

What is the general appearance of GSR?

Aggregate

Answer 5

• 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.

Question 6

When taking GSR samples from a suspect what should you try ensure?

Answer 6

• 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.

Question 7

Where should biological samples be stored?

Degrading

Answer 7

All biological GSR samples to be refrigerated immediately to prevent biological action degrading any nitrate compounds.

Question 8

What additional GSR samples can be taken with permission?

Answer 8

• 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.

Question 9

What can pathologists swab post-mortem? GSR

Answer 9

Pathologists can swab sinuses and recover mucous post-mortem.

Question 10

Where are the hand-sampling areas? (GSR)

Answer 10

• 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.

Question 11

How should GSR sampling from a suspect’s hand be done?

Answer 11

• 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.

Question 12

What anti-contamination procedures should be carried out for GSR?

Equipment, assessment, contamination, collection, PPE

Answer 12

• 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

Question 13

What anti-contamination procedures should be carried out for GSR? (2)

ASAP, deviations, clean area, integrity, gloves, monitor

Answer 13

• 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.

Question 14

What should you do with GSR at close range?

Dyes

Answer 14

• 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.

Question 15

What should you do with GSR at long range?

Deposits, wipe ring

Answer 15

• 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.

Question 16

What can you do with a GSR discharge pattern?

Analysed, test pattern, conditions

Answer 16

• 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.

Question 17

What is the Greiss test?

Explosive materials

Answer 17

• 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.

Question 18

What is the sodium rhodizonate test?

Answer 18

The sodium rhodizonate test is a chemical metal
deposition test which suggests the presence of lead

Question 19

When is the sodium rhodizonate test performed?

Answer 19

It can be performed after the Greiss test and involves spraying a 1% solution of the reagent in distilled water onto the test surface.

Question 20

What colours does the sodium rhodizonate test give?

Answer 20

• 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.

Question 21

What do a positive test from the sodium rhodizonate and Greiss test suggest?

Answer 21

• A positive result from this test and the Greiss test is strong evidence that a firearm has been discharged.
• Independently, the two tests do not represent such strong evidence.

Question 22

Chemical analysis of GSR…

Answer 22

Chemical analysis of GSR is almost exclusively restricted to the inorganic (metallic) residues, which are most strongly linked to the primer-related residues.

Question 23

How can inorganic residues from GSR be analysed?

Answer 23

• Inorganic residues can be interrogated using:
  o Scanning Electron Microscopy-Energy Dispersive X-ray analysis (SEM-EDX)
  o X-ray Fluorescence (XRF)
  o Atomic Absorption Spectroscopy (AAS)

Question 24

How can organic residues from GSR be analysed?

Answer 24

• Far less work is done on the organic components, which come largely from the propellant composition (NC/NG) but can be analysed by:
  o FTIR, Raman, GC-MS

Question 24

What are the two types of mixtures encountered for primers?

Answer 24

• Mercuric (rather dated now):
  o Mercury Fulminate
  o Barium Nitrate
  o Antimony Sulphide
• “Sinoxid” formulation (most common):
  o Lead Styphnate (possibly with other lead
  compounds)
  o Barium Nitrate
  o Antimony Sulphide
• These may contain other additives too (binders, sensitisers, frictionators etc.)
• Other less harmful primers also exist

Question 25

What is the function of Barium nitrate (BaNO3) in primers?

Answer 25

Barium nitrate (BaNO3) acts as an oxidiser to increase the heat of ignition.

Question 26

What is the function of Antimony Sulphide in primers?

Answer 26

Antimony Sulphide (Sb2S3) acts as the fuel in the ignition process. It also acts a “frictionator” during ignition.

Question 27

What is the purpose of Mercury Fulminate or Lead Styphnate in primers?

Answer 27

• Mercury Fulminate (Hg(CNO)2) or Lead Styphnate (C6HN3O8Pb) acts as the explosive to drive the ignition process.

Question 28

What are the positives of using SEM-EDX to analyse GSR samples?

Answer 28

• The technique is non-destructive.
• Minimal sample preparation is necessary.
• Individual particles can be analysed.
• The morphology of particles can be examined.
• GSR can be identified with a high level of confidence based on the elemental composition and morphology.
• Highly effective and fairly rapid automated systems have been developed for particle detection and classification.

Question 29

What are the different classifications of GSR particles?

Answer 29

• Characteristic of GSR
• Consistent of GSR
• Commonly associated with GSR

Question 30

What are particles characteristic of GSR?

Answer 30

Particles classified as ‘characteristic of GSR’ have compositions rarely found in particles from any other source.

Question 31

What are particles consistent with GSR?

Answer 31

• Particles classified as ‘consistent with GSR’ have compositions that are also found in particles from a number of relatively common, non-firearm sources.
• Particles within this group are produced through the operation of a variety of processes, equipment or devices and can be found in the environment with varying levels of frequency.

Question 32

What are particles commonly associated with GSR?

Answer 32

• Compositions that are also commonly found in environmental particles from numerous sources.
• However, when present, in addition to particles that are characteristic of, and/or consistent with GSR, these particles can be of significance in the interpretation of a population of particles and, consequently, the likelihood that that population is GSR.
• In isolation, however, such particles have little significance in examinations for GSR.

Question 33

Why is knowing particle populations important in GSR?

Answer 33

This is extremely important so that the evidential importance of each particle and the overall sample can be assessed and presented to the court.

Question 34

What is the peak height for a major additional component for sinoxid primers?

Answer 34

A MAJOR additional component has a peak height greater than 30% of the highest peak in the EDX spectrum.

Question 35

What is the peak height for a minor additional component for sinoxid primers?

Answer 35

A MINOR additional component has a peak height between 10% and 30% of the highest peak in the EDX spectrum.

Question 36

What is the peak height for a trace additional component for sinoxid primers?

Answer 36

A TRACE additional component has a peak height less than 10% of the highest peak in the EDX spectrum.

Question 37

What has to be true in order for the values of major, minor and trace additional components to be taken into account?

Answer 37

The thresholds are usually based on the relative
peak sizes for the L-transitions for Barium and any values should all be greater than the limit of detection for the instrument in order to be
considered.

Question 38

What must characteristic particles of GSR contain? (Sinoxid primers only!)

Answer 38

o Lead
o Antimony
o Barium

Question 39

What are additional elements often found in major, minor and trace amounts in characteristic GSR particles?

SCACT

Answer 39

• Silicon,
• Calcium,
• Aluminium,
• Copper,
• Tin

Question 40

What are additional elements often found in minor or trace amounts of characteristic GSR particles?

ISZPCPN

Answer 40

• Iron,
• Sulphur,
• Zinc,
• Potassium,
• Chlorine,
• Phosphorus,
• Nickel

Question 41

What compositions would particles consistent with GSR have?

BCS

Answer 41

Any of the following:
o Barium, Calcium, Silicon (with no more than a trace of Sulphur)
o Antimony, Barium (usually with no more than a trace of Iron or Sulphur)
o Lead with levels of Antimony greater than trace amounts
o Barium, Aluminium
o Lead, Barium

Question 42

What could commonly associated with GSR particles include?

Answer 42

o Lead with only trace levels of Antimony
o Lead
o Antimony
o Barium (in the absence of Sulphur)

Question 43

What additional elements may be found in particles commonly associated with GSR?

Answer 43

• Silicon,
• Calcium,
• Aluminium,
• Copper,
• Trace amounts of: Iron, Sulphur, Phosphorus, Zinc, Nickel (in conjunction with Copper and
  Zinc), Potassium, Chlorine and Tin

Question 44

What can cause false positives in GSR analysis?

Answer 44

• Vehicle airbags incorporate a primer device
• Fireworks & pyrotechnics
• Car break pads

Question 45

How can false positives from car airbags be ruled out from GSR?

Unusual, non-primer particles

Answer 45

• Most of the airbag primer residue contains elements unusual to GSR as well as lead, antimony, and barium.
• Furthermore, many thousands of non-primer particles, characteristic of airbag residues but foreign to GSR, are also expelled from the airbag on deployment.

Question 46

How can false positives of GSR caused by fireworks and pyrotechnics be ruled out?

Answer 46

• Most particles generated from the ignition of fireworks products contain elements not typically found in GSR, such as magnesium and/or other
  elements present in levels not generally seen in GSR (for example, elevated levels of chlorine and potassium).
• A very small proportion of particles generated, however, have simple three-component (lead, antimony, and barium) compositions.
• However, the rare instances of firework particles found with lead, antimony, and barium have not been found with spheroid morphology.

Question 47

How can fireworks caused false positives of GSR?

Answer 47

• The morphology of firework particles commonly shows the characteristics of having been formed in very high temperatures.
• A very small proportion of particles generated, however, have simple three-component (lead, antimony, and barium) compositions.

Question 48

What problems can pyrotechnic mixtures cause in terms of GSR?

Answer 48

• Pyrotechnic mixtures that contain aluminium powder and barium nitrate (in addition to various other compounds) can give rise to some spherical particles containing barium and aluminium.
• Such particles are also commonly generated from firearm ammunition primers rich in aluminium and barium nitrate.
• Occasionally, aluminium-barium particles created by pyrotechnics can be indistinguishable to those generated by certain ammunition.

Question 49

How can car break pads cause false positives in terms of GSR?

Answer 49

• Car brake pads containing compounds of lead, antimony, and barium have been used by some vehicle manufacturers.
• The friction caused by the application of the brakes results in the shedding of fragments and particles from the brake pads.
• Some of these particles contain lead, antimony, and barium, usually with a variety of other elements.
• These particles can resemble GSR when the other elements that are characteristic of the brake pads are absent and friction can
  result in more intimate mixing of the lead, antimony, and barium components.

Question 50

How can car brake pads be ruled out from GSR?

Answer 50

• Most particles can be clearly distinguished from GSR due to the presence of elements rarely found in GSR, and/or elements present in levels not generally seen in GSR, such as elevated levels of iron.
• Most of these particles are irregular in form and heterogeneous in composition (that is, separate lead, antimony, and barium zones are
  generally observed).