Developing STR Profiles from Fired and Unfired Brass and Nickel-plated Cartridge Cases
Meghan Troy, BS*, Arcadia University, 450 S. Easton Rd., Glenside, PA 19038; Christian Westring, PhD, NMS Labs, 3100 Stratford Av., Willow Grove, PA 19090; Allen Stewart, MS, Swede and Airy Streets, Norristown, PA 19401 ; Jill Yeakel, MSFS, 115 Purple Heart Dr., Dover AFB, DE 19904;; Heather Mazzanti, MSFS, Arcadia University, 450 S. Easton Rd., Glenside, PA 19038
After attending this presentation, attendees will be aware of the likelihood of obtaining STR DNA results from nickel-plated and brass cartridge cases, both unfired and fired.
This presentation will impact the forensic community by examining the ability forensic biologists have to recover useful DNA profiles from fired and unfired cartridge cases depending on metal composition by analyzing and comparing both nickel-plated and brass cartridge cases.
DNA is transferred to ammunition when it is being loaded into a firearm by shedding skin cells found in the oil and sweat residues of fingerprints. However, obtaining complete DNA profiles from cartridge cases can be difficult because the DNA is present in small quantities or has been degraded.Many members of the forensic science community believe that the amount of DNA that can be recovered depends on the types of cartridge caseused. It is commonly held that there is less of a chance of obtaining useful DNA profiles from brass cartridge cases thanfrom nickel-plated or aluminum cartridge cases, however this is not well documented in published literature. There are many theories as to why it could be more challenging to recover DNA from brass cartridge cases in comparison to nickel-plated or aluminum cartridge cases, however these theories have either been disproved or not thoroughly tested.This research will use a sample size of 200 cartridge cases to determine the frequency with which nuclear DNA can be recovered from brass and nickel-plated cartridges that have been both fired and unfired.
Of the 200 cartridge cases used in this study, 100 were brass and 100 were nickel-plated. All cartridge cases were the same caliber, 45mm. The cartridge cases were handled only long enough to load into a 10 round magazine. Half of these cartridges were fired and half were unloaded from the magazine manually. The fired and unfired cartridges were swabbed for DNA using a double swab technique. All samples were extracted using a Qiagen EZ1 automated large volume protocol, quantitated using real-time quantitative PCR, amplified using the PromegaPowerPlex 16 HS Amplification Kit and analyzed using the ABI 310 Genetic Analyzer. No statistically significant difference in quantity of DNA recovered from cartridge cases as a function of metal type was observed. During quantitation, detectable levels of DNA were recovered 36% of the time from brass cartridges and 12% of the time from nickel-plated cartridges. The unfired brass cartridges yielded partial DNA profiles 36% of the time while unfired nickel-plated cartridges yielded partial DNA profiles only 12% of the time. No profiles could be obtained from the remaining brass and nickel-plated cartridges. This study demonstrates to the difficulty of producingDNA profiles from cartridge cases regardless of metal type. Work to optimize DNA recovery based on collection technique is currently in progress.