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.

Collection and direct amplification methods using the GlobalFiler™ kit for DNA recovered from common pipe bomb substrates.

When analyzing DNA from exploded pipe bombs, quantities are often in trace amounts, making DNA typing extremely difficult. Amplifying minute amounts of DNA can cause stochastic effects resulting in partial or uninterpretable profiles. Therefore, the initial DNA collection from "touch" evidence must be optimized to maximize the amount of DNA available for analysis. This proof-of-concept study evaluated two different swab types with two direct amplification strategies to identify the most effective method for recovering DNA from common pipe bomb substrates. PVC and steel pipes, electrical tape, and copper wire spiked with epithelial cells were swabbed with cotton or microFLOQ® Direct Swabs and amplified directly or via a pre-treatment prior to STR amplification. Not only was the microFLOQ® Direct Swab protocol the quickest method with the least risk of contamination, but in combination with direct amplification, the microFLOQ® Direct Swabs also generated the most complete STR profiles.

Analysis of DNA from post-blast pipe bomb fragments for identification and determination of ancestry.

Improvised explosive devices (IEDs) such as pipe bombs are weapons used to detrimentally affect people and communities. A readily accessible brand of exploding targets called Tannerite® has been identified as a potential material for abuse as an explosive in pipe bombs. The ability to recover and genotype DNA from such weapons may be vital in the effort to identify suspects associated with these devices. While it is possible to recover DNA from post-blast fragments using short tandem repeat markers (STRs), genotyping success can be negatively affected by low quantities of DNA, degradation, and/or PCR inhibitors. Alternative markers such as insertion/null (INNULs) and single nucleotide polymorphisms (SNPs) are bi-allelic genetic markers that are shorter genomic targets than STRs for amplification, which are more likely to resist degradation. In this study, we constructed pipe bombs that were spiked with known amounts of biological material to: 1) recover "touch" DNA from the surface of the device, and 2) recover traces of blood from the ends of wires (simulated finger prick). The bombs were detonated with the binary explosive Tannerite® using double-base smokeless powder to initiate the reaction. DNA extracted from the post-blast fragments was quantified with the Quantifiler® Trio DNA Quantification Kit. STR analysis was conducted using the GlobalFiler® Amplification Kit, INNULs were amplified using an early-access version of the InnoTyper™ 21 Kit, and SNP analysis via massively parallel sequencing (MPS) was performed using the HID-Ion Ampliseq™ Identity and Ancestry panels using the Ion Chef and Ion PGM sequencing system. The results of this study showed that INNUL markers resulted in the most complete genetic profiles when compared to STR and SNP profiles. The random match probabilities calculated for samples using INNULs were lower than with STRs when less than 14 STR alleles were reported. These results suggest that INNUL analysis may be well suited for low-template and/or degraded DNA samples, and may be used to supplement incomplete or failed STR analysis. Human identification using SNP analysis via MPS showed variable success with low-level post-blast samples in this study (<150pg). While neat DNA samples (6µL input as recommended) resulted in <50% of SNP calls, samples that were concentrated from 15µL to 6µL (15µL was added for STR and INNUL typing) resulted in more complete SNP profiles. Five out of six blood samples recovered from the wires attached to the pipe-bombs resulted in the correct ancestry predictions.