Casework comparison of DNA sampling success from steering wheels and car seats in tropical Australia

Investigations of unlawful use of motor vehicle (UUMV) offences often rely on detection of the offender's DNA inside the vehicle. Steering wheels are likely to retain the DNA of a recent driver; however, they often recover insufficient DNA for forensic DNA profiling or complex mixed DNA profiles unsuitable for comparison. In contrast, samples taken from the driver's side seat often included the recent driver's profile, with less DNA from other individuals. Further, in warmer climates, offenders are likely to dress in lightweight clothing, including shorts, which increases skin contact with car seats, particularly during the warmer months. Thus, to test the suitability of sampling car seats in comparison with steering wheels in a casework context, we employed a paired sampling approach to every suitable vehicle examined by forensic officers in a tropical Australian regional city over a six-month period. There was a significant difference between the overall DNA sampling results from car seats and steering wheels; however, there was little difference in the numbers of uploadable profiles or offender identifications between the sampled areas. These data contribute substantially to our knowledge of DNA transfer under real-world conditions and inform operational practices aimed at maximizing evidence recovery from crime scenes.