Genetic profiling from 9 mm fired cartridge cases over 30 days

Fired cartridge cases are common materials found at crime scenes and, for the most part, are used for Forensic Ballistics analysis. We aimed to evaluate the feasibility of recovering DNA profiles from 9 mm cartridge cases over 30 days. Therefore, 27 fired cartridge cases were manipulated by three volunteers in total and analyzed after three-time intervals: 3, 8, and 30 days. Volunteers were asked to handle the ammunition as they would daily. However, they were not encouraged to hold and manipulate the ammunitions extensively, as this procedure does not represent a real-life situation. DNA samples were obtained with an EZ1 DNA Investigator kit, qPCR was performed with Investigator Quantiplex Pro RGQ kit, and Powerplex Fusion 6 C was used for STR analysis. Real-time PCR analysis showed that 85% of the 27 samples were degraded and no inhibition was detected. The DNA mean concentration was 0.3 pg/µl for each time interval, and the standard error was 0.1 pg/µl, 0.09 pg/µl, and 0.1 pg/µl for the three-time corresponding intervals. The Kruskal-Wallis test indicated p = 0.6, which meant no statistical differences between the samples analyzed. STR analysis resulted in a success rate of 16% for intervals of 8-days and a success rate overall of 7%. No DNA profile was obtained from the 3-and 30-day-old samples. Air relative humidity was 75% on the day of experimentation. Our results could contribute to understanding the factors affecting genetic profiles from fired cartridge cases: 3-day-old samples already showed 77.8% degradation. Once moisture catalyzes the metal oxidation processes, relative humidity and the metallic surface of cartridges may play an important role. We assume that time interval may not be the main factor regarding DNA analysis success, and low success rates are more likely to be obtained for real-life scenarios.