An assessment of firework particle persistence on the hands and related police force practices in relation to GSR evidence

In a previous study by Grima et al. Sci. Justice 52 (1) (2012) 49, it was shown that background particles can aid in the exclusion of firework particles which are indistinguishable from GSR. Issues relating to the persistence of such particle populations were presented. The scope of this project was to examine persistence on the hands in the context of possible post-display scene contamination and how this can affect GSR evidence, especially in light of possible GSR/firework mixtures. Persistence was investigated by recovering firework residues eight hours post-display following contact of the hands with bedding. In addition, particle profiling was carried out using SEM-EDX. Firework particle populations exhibited strong persistence in all displays, with not less than 667 particles persisting in each scenario. This factor challenges GSR evidence, especially if personnel stationed at display sites enter scenes of crime or come into contact with suspects after a display. A survey of UK police force practices following firework displays showed that authorities are not aware of the impact particle transfer may have on GSR evidence. Recommendations for the implementation of basic hygiene practices for particle transfer control have also been made.