Secondary and subsequent DNA transfer during criminal investigation

DNA detection of a temporary and original user of an office space

“…The temporary occupier was detected in 23 of 75 (31 %) profiles: 0x as the only contributor, 3x as a major, 8x as a majority contributor and 12x as a minor contributor. When the temporary occupier was observed as a majority or major contributor, the LRs ranged from 80 to 2 × 10 22 and included: 6x samples in O3, 5x in O4 and none in either O1 or O2 (Table 2). In 6 of the 11 profiles where the temporary occupier was the majority or major contributor (8 % of interpretable profiles), the office owner was also present as a minor contributor ( Table 2).…”

A review of trace “Touch DNA” deposits: Variability factors and an exploration of cellular composition

“…DNA has been demonstrably transferred by handling both with and without gloves [97], from a range of items to both secondary and tertiary objects [98]. The transferred DNA may yield profiles ranging in quality from non-existent to complete and database-uploadable [97,98], following either prolonged or brief social contact [99], leaving unpredictability (see Table 2).…”

Cale CM, Earll ME, Latham KE, Bush GL. Could Secondary DNA Transfer Falsely Place Someone at the Scene of a Crime? J Forensic Sci 2016;61(1):196–203

“…Other studies examining the transfer of "touch" DNA in less controlled scenarios, considered more realistic examples of secondary transfer rates, have observed the transferred DNA as the major or only component to the profile on far fewer occasions, if at all:~2.8% in studies where the source of the transferred DNA was known (9-12);~1.4% in studies where the source of the transferred DNA was unknown (13,14). Several other studies allude to the detection of secondarily transferred DNA from known and/or unknown sources within the samples obtained, but provide insufficient information with respect to their presence forming a minor or major component of the profile, and in the case of foreign alleles, whether they originated from a single or multiple sources (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26).…”

“…Further, Cale et al (1) posit that the transfer of DNA through an intermediary has not been systematically evaluated with current technology. Studies have provided empirical evidence of secondary (and further, including tertiary and quaternary) transfer (9,10,16,27), have investigated variables that may affect the transfer and subsequent detection of touch DNA (7,8,13,18,20,(22)(23)(24)28,29), have provided casework relevant examples and simulations to model the possible effect of transfer on conclusions (9)(10)(11)14,16,17,21,(30)(31)(32), and have provided statistical models to evaluate the possibility of transfer (33)(34)(35). Such studies have been conducted with various autosomal STR methods employed in forensic biology, including the current sensitive technologies, and, more recently, with alternate methods such as mRNA profiling (18,21).…”

“…Ultimately, DNA should not be used as the sole form of evidence, but should be presented as one of multiple pieces of evidence that may assist the trier of fact. Reliance upon DNA alone can result in erroneous conclusions, not just due to transfer, but also contamination and adventitious matching (16,36,(43)(44)(45).…”