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Abstract
Gun-related crimes are the cause of many homicides and injuries every year across the United States. According to the Federal Bureau of Investigation (FBI) statistics, firearms were used in 68% of murders, 41% of robberies, and 21% of aggravated assaults in 2011 alone. Cartridges and casings left on the scene often link shootings to a firearm and many times are the only evidence. Traditional swabbing of fired cartridge casings (FCCs) has yielded usable profiles only approximately 1-2% of the time, causing many laboratories to refrain from processing FCCs.
A method for collection of the cellular material from the FCCs for downstream DNA analysis was developed and evaluated. Chelation filtration is a simple, easy-to-perform, two-step filtration method using Chelex resin in the initial incubation step and only requires a vacuum device along with two filter devices. The process does not create any need for alterations to downstream DNA analysis. Comparisons of the Chelation filtration method (N=20) to traditional swabbing (N=20) were conducted and the quantity of DNA recovered (ng) as well as the percentage of expected alleles observed was evaluated using A-NOVA analysis, resulting in 40% (P
An anecdotal study of 122 cases was performed to evaluate the effectiveness of the Chelation filtration method on real casework evidence, where 21 interpretable DNA profiles were obtained yielding 5 CODIS matches. With the assistance of STRmix analysis, over 50% of those profiles were eligible for statistical calculations and STRmix was also used to deduce profiles for CODIS entry. The Chelation Filtration method can be an invaluable tool to help solve gun crimes where there is little to no other evidence besides FCCs.