Crimes involving firearms are extremely common, and it is therefore important that law enforcement be able to identify the individual who fired a weapon. Previous researchers have shown that DNA recovered from spent casings can be used to identify the loader of a firearm, however success has been highly variable, largely due to the wide variety of factors that have the potential to influence DNA on spent casings. The goal of this research was to test several such factors, including loading/firing order, pre-processing spent casings for fingerprints, cartridge caliber, swabbing strategy, and analysis technique. Forty caliber cartridges loaded by volunteers were fired and the casings were collected, two-thirds of which were fumed with cyanoacrylate to examine the influence of fuming on DNA recovery and analysis. Volunteers also loaded 0.45 and 0.22 caliber cartridges, which were swabbed individually or cumulatively in sets of three. DNA was extracted, quantified, and STRs were amplified using a MiniFilerTM and/or Fusion amplification kit. The HV1 and HV2 regions of mtDNA were also amplified. Cyanoacrylate fuming was found to have a negative effect on DNA recovery and analysis. Significantly more DNA was recovered from 0.45 caliber casings than from 0.22 caliber casings. Cumulative swabbing yielded more DNA and handler alleles than individual swabbing, although it also resulted in a higher number of mixtures. Fusion outperformed MiniFilerTM as an STR amplification kit, and mtDNA was successfully sequenced for all casings tested. Loading order was the only factor that did not have a significant effect, and as such all other variables should be strongly considered when DNA analysis from spent casings is undertaken.
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