“The amount of GSR particles, 2 component particles and 1 component particles found on a sample does not dictate whether or not an incident is more or less likely.”
“Because of these factors (and others) the amount of particulate found on a sample is not an indication of likelihood or probability. The more GSR found on an individual does not mean he or she is more likely to have discharged a firearm. Conversely, the less GSR found on an individual does not mean he or she is less likely to have discharged a firearm.”
“The number however, in the absence of 3 component GSR particles, does not alter the likelihood of whether or not they originated from a firearm.” (Answer 1) and further states that there is no scientific basis to suggest that the greater the number of one-component and two-component particles found, the more likely it is that they came from a gun (Answer 11). It is also interesting to note that paragraph 5.5.3 of the current ASTM reporting guidance states that the number of confirmed two-component particles cannot be used to determine whether or not they come from a non-firearm source. On the other hand, there is material which supports the submission by Mr Poole QC on behalf of the respondent that the judge was right on this point and the number of one-component particles increases the probability that a population of particles is the product of gunshot discharge. Thus, for example, the SWGGSR Guide for Primer Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X -Ray Spectrometry (2011) states: “The probability that a population of particles is GSR increases significantly with … The presence and number of particles commonly associated with GSR.”