Persistence of DNA deposited by the original user on objects after subsequent use by a second person

There is a paucity of data regarding the persistence of DNA from prior user of an object after, its use by another person. To acquire a greater understanding of persistence we performed controlled, experiments encompassing over 179 objects that had only been used by one individual for an extended, period before used by a 2nd person for various but known duration. Our findings show that the profile, percentage contribution of the 1st user relative to the 2nd user of an object declines in a linear manner, over time. The retrieval of the profile of the initial user of the object is dependent on the type of, substrate and use of the object. When considering a hard non-porous object the 1st user's profile, percentage contribution drops ∼50% immediately upon use by a 2nd person and drops to ∼15% after, 90 min. When considering a soft porous object the 1st wearer's profile contribution remains, higher than that of the 2nd wearer during the first 10 h of wear by the 2nd wearer and still, accounts for ∼12% after 96 h. This substrate associated difference was also observed in an, assessment of a wide range of personal objects used by 2nd users for different durations. Particular, areas of certain objects were more likely to retain a greater proportion of the 1st user's DNA than other, areas. Alleles of unknown source were present on the majority of objects but rarely exceeded 10% of, the total profile. Greater knowledge of persistence will inform investigators regarding the likelihood of, detecting a profile of a particular individual based on the type of object and its history, and assist with, identifying the best areas of an object to target for DNA sampling.