firearms analysis Flashcards
what are the three classifications of p-GSR evidence
unique
characteristic
indicative classification
unique p-GSR evidence
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
characteristic p-GSR evidence
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
indicative classification p-GSR evidence
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
at high levels
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
challenges to the result
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
in the absence of contra-indicators
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
innocent possibilites to explain GSR presence
Firing of a weapon or blank firing device
Aerosol transfer
Contact with a fired weapon
Secondary or even tertiary transfer
does the suspect have access to legally held weapon?
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
does the suspect have access to a blank firing device?
- Blank firing grenades, bird scarers or blank firers will produce GSR
does the suspect have contact with those who do have a legally held weapon or blank firing device?
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
has the suspect had contact with a firearm
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
was the suspect present at the scene at any point?
- Aerosol transfer is a distinct possibility and the presence of GSR does not mean that the suspect is the firer of a weapon
how was the arrest made
- 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?
amount of GSR
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)
quantity
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
generally accepted significance based on levels of p-GSR
Low: 1-2 Primer particles
Moderate: 4-12 primer particles
High:13-50 primer particles
Very High: 50+ particles
generally accepted significant based on levels of o-GSR
Low: 2-20ng of propellant
Moderate: 21-200ng of propellant
High: 201-2000ng of propellant
Very High: Greater than 2000ng of propellant
persistence on hands
4 hours
persistence on face
6 hours
persistence on hair
12 hours
persistance on clothing
up to 24 hours
GSR found after typical persistence times is more likely to be the result of another event
Clearly GSR found on hands 24hrs after discharge is odd so think again
Possibly redistribution of residue from another surface
Secondary or tertiary transfer
GSR found in pockets
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
GSR found on the back of a garment
may indicate proximity to firing and could be used to help understand a suspect’s role and relative position in some cases
GSR found on the waistband
may be the result of holstering a weapon in trousers but this material is lost rapidly due to skin/material friction
We cannot even state which hand was used to fire the weapon
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
range and proximity
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
secondary transfer
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
possible secondary transfer
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
police
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
