An improved process for the collection and DNA analysis of fired cartridge cases

Improvements to the DNA analysis of fired cartridge cases have been made in recent years, yet successful analysis of this important evidence type remains difficult. In this study, we describe both a novel device for the collection and transport of fired cartridge cases and a new DNA recovery method that incorporates a rinse-and-swab technique. This technique combines two different types of swabs and a rinse solution with additives that reduce the degradative effects that copper has on DNA. The new recovery method yielded approximately threefold more DNA than the traditional double swab method and reduced the evidence of degradation. After validation, we estimated the real-world success rate of obtaining DNA profiles suitable for comparison with the rinse-and-swab method by testing over 100 cartridge cases collected from crime scenes. Approximately 67 % of the time (8 of 12), at least one DNA profile suitable for comparison was obtained from fired cartridge cases assumed to be associated with a single firearm using the collection device and the rinse-and-swab method when the fired cartridge cases were collected within 24 h.