Transfer and persistence of DNA on items routinely encountered in forensic casework following habitual and...

Empirical data obtained from controlled experiments is necessary to ensure that sound expert opinion evidence is provided regarding transfer and persistence of DNA in criminal proceedings. Knowledge in this area is also required at the outset of criminal investigations, to ensure that the proposed examinations can assist with answering questions that are relevant to forensic investigations. This study aimed to provide such data by examining the relative and absolute quantities of DNA deposited on items that are routinely submitted to the forensic laboratory by a habitual user, defined as someone who used it for ~1 week, and a subsequent one-time user. We found that the quantity of DNA deposited on routine household items spanned a broad range. The habitual user's DNA was detected on most items as the major donor, regardless of whether it was subsequently handled by another person for a short period of time. The one-time, short duration, user's DNA was detected on approximately two thirds of the items, albeit typically at quantities lower than the habitual user. Most of the household items we examined also had detectable DNA deposits from at least one other, unknown individual, typically in low quantities. Attempts to clean non-porous items with readily available household cleaners were partially effective but failed to completely eliminate detectable DNA from a habitual user in most cases.