Efficacy of "touch" DNA recovery and room-temperature storage from assault rifle magazines

Crimes committed with assault rifles are becoming increasingly prevalent in the United States. In the absence of other evidence, DNA analysis can often provide informative leads. Unfortunately, any DNA transferred to rifle components left behind at a crime scene is likely to be low in quantity and/or quality. Furthermore, collected evidence is unlikely to be processed immediately and may require storage. Long-term storage can subject DNA to damage and degradation, which ultimately affects DNA profile interpretation and may prevent the identification of potential suspects. This study assessed the ability of a new swab storage device, the SwabSaver®, to preserve "touch" DNA from AR-15 magazine rifles using three different collection devices. Three volunteers loaded bullet cartridges into plastic polymer and aluminum AR-15 magazines. DNA was collected with traditional cotton swabs, layered cotton paper swabs, or nylon-flocked swabs. Collection devices were then stored at room-temperature for up to two months in either the SwabSaver® device or an empty centrifuge tube. The results suggest that substrate and swab type had less of an effect on profile completeness than storage type. Furthermore, SwabSaver® storage yielded DNA quantities comparable to "touch" DNA extracted after 24 h.