Optimized Method for Maximizing DNA Yield from Fired Cartridge Casings

Crimes involving guns have become increasingly prevalent in our society and investigative techniques for solving these crimes have been limited due to several factors.  One factor is that the evidence left behind is commonly comprised of spent cartridge casings or stray bullets.  These items are typically analyzed with firearms comparisons since DNA analysis has not proven to be successful in the past when using the typical collection technique of swabbing.  Some reasons for this include the fact that only a limited number cells are deposited on bullets when loading a gun, other factors such as the shedder status of the person handling the bullets and the environmental conditions.  Many laboratories have instituted policies where spent casings are not analyzed for DNA and investigators are left with firearms analysis only.  The Broward Sheriff’s Office Crime Laboratory and Crime Scene Unit have worked together to optimize a DNA collection method that allows for approximately 41% higher DNA recovery when compared to swabbing techniques and yielded DNA profiles consisting of approximately 68% more alleles.  Briefly described is the optimized collection method itself, data results from several different controlled studies utilizing hundreds of bullets as well as observed results from forensic casework.  This method is simple to implement and does not affect downstream DNA processing.