Prevalence of DNA from the driver, passengers and others within a car of an exclusive driver

Cars are often sampled for DNA to help identify occupants and their possible location(s) within the car. While DNA from the frequent driver is likely to accumulate over time, DNA from previous and/or subsequent occupants, and those whose DNA has inadvertently been transferred to the car, may also contribute to any samples collected. This study investigates how much DNA resides on various sites within cars, and who might contribute to these samples. A total of 35-36 sites, internal and external, were targeted within four cars with sole long-term drivers. In addition to the car keys, sample sites included the exterior and interior door handles (driver and passenger sides), through to the internal compartments (driver side, middle area and front passengers' side). Reference samples were collected from the exclusive drivers, their co-resident partners and, where possible, recent passengers. The driver was always observed as a contributor in DNA profiles from the driver's side and, in most instances, was the sole, major or majority contributor to the profile. The driver was also observed as a major, majority or minor contributor at several sites on the passenger side. DNA of known recent passengers, close associates of the driver and unknown individuals was collected from many sites on both the driver and passenger sides. These findings may assist in sample targeting within cars and in the evaluation of DNA evidence when propositions relate to the activities performed.