firearms analysis

Question 1

what are the three classifications of p-GSR evidence

Answer 1

unique

characteristic

indicative classification

Question 2

unique p-GSR evidence

Answer 2

no longer used in UK parlance

Particulate once believed to be found only from the detonation of a primer

Generally of Pb-Ba-Sb type (Type I)

Studies have shown some alternate sources for this type of GSR – Brake linings

Question 3

characteristic p-GSR evidence

Answer 3

Strongest term used in UK parlance

Particulate extremely strongly associated with firearm discharge

This is almost definitely GSR

In general uncommon in the environment

May have alternate sources but it’s probably GSR

Evidential strength depends upon amounts present and any contra-indications but these are perhaps activity level considerations

Question 4

indicative classification p-GSR evidence

Answer 4

Particulate fairly strongly associated with firearm discharge

Its probably GSR but might not be

Particulate has alternate sources

Not very common environmentally

It is probably GSR, but it could be something else and therefore

Not always reported, but may lend supporting evidence

Question 5

at high levels

Answer 5

Pb and Pb-Sb could be bullet/pellet debris, but it could be solder!

Ba-Al, Ba-Ca-Si, Ba-Sb and Sn-Sb could be GSR, but some combinations are produced by fireworks!

That said, size and morphology of firework residue generally inconsistent with p-GSR

Question 6

challenges to the result

Answer 6

Defence assertion – The residue is not GSR

Characteristic GSR has fewer alternative sources

• Therefore the possibility of an alternative source is less likely
• Environmental sampling may be appropriate to test the hypothesis

Indicative GSR has more potential alternative sources
- Therefore the possibility of an alternative source becomes more likely

Question 7

in the absence of contra-indicators

Answer 7

It may be reasonable to suggest that the residue present is GSR

Especially if it is characteristic and at a reasonable level

This doesn’t necessarily indicate the suspect having fired a weapon, just that samples obtained contain what is believed to be GSR

What it means within the context of the case is the next thing to think about… But in the mean time

Apply extreme caution if indicative or at low level

Such results may not be reported in some cases

Barry George GSR evidence has dented confidence in GSR evidence

Re-evaluate as further information becomes available

Question 8

innocent possibilites to explain GSR presence

Answer 8

Firing of a weapon or blank firing device

Aerosol transfer

Contact with a fired weapon

Secondary or even tertiary transfer

Question 9

does the suspect have access to legally held weapon?

Answer 9

This could be their own weapon – over 500,000 firearms owners in the UK

A borrowed/hired weapon – Possibly the property of a gun club

Involvement in clay, rough shooting or beating

This would be a quite legitimate source of GSR

Question 10

does the suspect have access to a blank firing device?

Answer 10

• Blank firing grenades, bird scarers or blank firers will produce GSR

Question 11

does the suspect have contact with those who do have a legally held weapon or blank firing device?

Answer 11

In the UK on average around 1/120 people own a firearm and this number increases significantly in rural areas

This contact may be overt or otherwise

Question 12

has the suspect had contact with a firearm

Answer 12

Clearly GSR is likely to be present on a firearm and is rapidly and easily transferred between a weapon and clothing

Handling a firearm may not be something the suspect will easily admit to

Question 13

was the suspect present at the scene at any point?

Answer 13

• Aerosol transfer is a distinct possibility and the presence of GSR does not mean that the suspect is the firer of a weapon

Question 14

how was the arrest made

Answer 14

• Was a bang-flash or similar pyrotechnics used?
• Were armed officers involved – Clearly firearms officers may well be covered in GSR?
• Is contamination a possibility?

Question 15

amount of GSR

Answer 15

The quantity of GSR present may well lend support particular hypotheses

This needs to be considered within the context of the elapsed time since firearm discharge (discussed shortly)

Question 16

quantity

Answer 16

Very High/High – May indicate recently fired weapon, in vicinity of recently fired weapon, contact with weapon

Moderate/High – As above but less recent

Low/Moderate – May indicate secondary/tertiary transfer, contamination

All taken in the concert with other factors

Question 17

generally accepted significance based on levels of p-GSR

Answer 17

Low: 1-2 Primer particles

Moderate: 4-12 primer particles

High:13-50 primer particles

Very High: 50+ particles

Question 18

generally accepted significant based on levels of o-GSR

Answer 18

Low: 2-20ng of propellant

Moderate: 21-200ng of propellant

High: 201-2000ng of propellant

Very High: Greater than 2000ng of propellant

Question 19

persistence on hands

Answer 19

4 hours

Question 20

persistence on face

Answer 20

6 hours

Question 21

persistence on hair

Answer 21

12 hours

Question 22

persistance on clothing

Answer 22

up to 24 hours

Question 23

GSR found after typical persistence times is more likely to be the result of another event

Answer 23

Clearly GSR found on hands 24hrs after discharge is odd so think again

Possibly redistribution of residue from another surface

Secondary or tertiary transfer

Question 24

GSR found in pockets

Answer 24

May be problematic due to lengthy persistence

GSR may remain in pockets for years under some circumstances even after washing

Treat such evidence with extreme caution

Question 25

GSR found on the back of a garment

Answer 25

may indicate proximity to firing and could be used to help understand a suspect’s role and relative position in some cases

Question 26

GSR found on the waistband

Answer 26

may be the result of holstering a weapon in trousers but this material is lost rapidly due to skin/material friction

Question 27

We cannot even state which hand was used to fire the weapon

Answer 27

There is little correlation between firing hand and GSR levels

In fact firing hand will often contain less GSR than non-firing hand

Dominant hand is used more and will therefore shed GSR more rapidly

Question 28

range and proximity

Answer 28

Logically residue deposition increases as we get closer to the place of firing

Primer residue tends to travel no more than 3m from the barrel

Unburned propellant may travel somewhat further

Question 29

secondary transfer

Answer 29

Contact with an object or person contaminated with GSR may result in transference – Secondary transfer

There is even limited evidence of tertiary transfer

In both scenarios, the level of transfer is logically likely to be low

Higher GSR levels are unlikely the result of secondary or tertiary transfer

Question 30

possible secondary transfer

Answer 30

Firer of a weapon – Legitimate or otherwise

Those in the vicinity of weapons discharge

Objects which were in the vicinity of weapons discharge

Objects handled by the firer of a weapon

Question 31

police

Answer 31

Arrests are more likely to have been made by firearms officers

These individuals are trained in use of firearms

Likely to be a source of potential GSR particulate

Studies in the US show that secondary transfer between firearms officers and suspect is extremely common

• Firearms chemists will always ask if firearms officers were involved
• Analysis of GSR present on officers may not match that found on the suspect
• Type VII found on suspect, police use type I ammunition
• This eliminates the police as a potential source in most cases