Trial by Fire: Comparing DNA Degradation in Blood versus Semen After Fire Exposure

Criminals have long used fire to try to destroy evidence of other crimes. Historically this cover-up attempt has had enough success that today investigators may assume evidence has either been consumed by the fire or ruined by the fire-fighting efforts. Yet research indicates evidence can endure fire and still yield partial or even full DNA profiles. However, there has been little investigation into the robustness of DNA from one biological fluid compared to another. This study examines whether fire degrades the DNA from blood more than the DNA from semen. The two biological fluids were exposed to fire, the DNA from these samples was extracted using Qiagen kits, and DNA degradation was quantified using a real-time polymerase chain reaction. DNA was quantified from 59 postfire samples plus 10 positive controls. Data analysis indicated the DNA degradation levels were not significantly different between blood samples and semen samples. However, DNA degradation levels varied significantly between samples on different substrates (nylon versus polyester).