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DNA transfer is a well-recognised phenomenon impacting the probability of detecting the presence of a particular source of DNA and thus the likelihood of the evidence given considered events within forensic investigations. Comprehensive study is lacking on variables associated with indirect DNA transfer without physical contact. Additionally, the drying properties of forensically relevant biological materials are under researched despite the recognised potential for these properties to affect DNA transfer. This study investigated the drying properties and indirect DNA transfer of dried blood, saliva, semen, vaginal fluid and touch DNA without contact deposited on two different non-porous hard substrates (melamine and glass) and two different porous soft substrates (polyester and cotton) by tapping (all substrates) and stretching (only fabric substrates) agitations. Different apparent drying trends were observed between the volumes, substrates and biological materials tested with substrate type generally having a greater influence than biological material. The rate and percentage of indirect transfer appeared to be dependent on agitation, substrate type, biological material and its drying properties. The outcomes of this study may assist those evaluating the likelihood of the evidence given proposed events during activity level assessments., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Drying properties of forensically relevant biological materials including saliva are lacking research despite being known to affect casework-relevant phenomena, including DNA transfer. We previously observed that saliva collected from someone chewing gum and deposited on various surfaces did not dry, raising questions about the effects of chewing gum on the drying properties of saliva. The DNA content of saliva samples under differing conditions is also not well known. This study investigated the drying properties and DNA content of saliva deposited on glass from samples collected before, during and after chewing gum. Samples taken before chewing gum dried the fastest and an inverse relationship between the time since chewing gum began and saliva drying time was found; as the time between the chewing and sample collection decreased, the drying time increased. All samples except those taken at the two minutes mark of chewing dried within the 96 h–27 days observation period. DNA yield initially decreased as chewing begun, then recovered during and after chewing, sometimes to be greater than the control sample. These observations contribute to our limited knowledge regarding variables affecting saliva samples. However, further research to facilitate activity level assessments regarding saliva samples is desirable. [ABSTRACT FROM AUTHOR]