Evaluation and Optimization of DNA Recovery and Amplification from Bullet Cartridge Cases

As submitted by the proposer: Cartridge cases are commonly encountered at crime scenes, however, DNA testing frequently fails to produce interpretable profiles. Common explanations for this include minimal DNA transfer; DNA destruction by heat of firing; PCR inhibition/DNA degradation from reactive metallic species in GSR or the cartridge case itself. The proposed research will optimize existing methods and evaluate emerging Next Generation Sequencing (NGS) approaches for the recovery and successful amplification of DNA from fired and unfired cartridge cases. This research will develop a robust approach for generating more complete genetic profiles using standard (not increased PCR cycle number) DNA profiling technologies. This work will also identify possible GSR or cartridge caseassociated inhibitors that may co-extract with DNA and propose solutions for circumventing such effects. This research has five core objectives: 1) Optimize a reliable method for maximizing the recovery and extraction of “touch type” DNA from metal cartridge cases. 2) Develop a robust protocol for DNA profiling of challenging samples based on existing recovery/extraction and emerging NGS technologies. 3) Identify possible co-eluting species from GSR or metal reactive species from the casings themselves that may compromise DNA profiling. 4) Demonstrate the reliability of the optimized protocols for bullet calibers commonly encountered in casework. 5) Develop appropriate and reliable Standard Operating Procedures for casework samples. Preliminary testing on brass and nickel-plated cartridge cases has yielded interpretable STR profiles from nearly 40% of samples. This represents a significant increase over existing methods. A broader range of methodologies will be applied to a larger and more diverse sample set to improve both the success rate and DNA profile quality. Pilot data have also identified a potential issue with a possible co-eluting GSR/metal-related species that is extraction technique dependant and significantly reduces genetic profile quality. This will be investigated over a wider range of extraction methodologies to characterize the responsible compound(s) and potential countermeasures. This project builds collaborations that bring together a team of skilled researchers and experienced practitioners. This work has the potential to significantly improve the potential to obtain interpretable genetic profiles from cartridge cases. It will provide practitioners with a readily transferable methodology for the analysis of challenging cartridge case evidence and a guide to the use of NGS technologies. In short, the successful completion of this research will provide the forensic community with a powerful tool to aid in criminal investigations. Findings will be presented at conferences, workshops and in professional journals. This project contains a research and/or development component, as defined in applicable law. ca/ncf