DNA testing of touch evidence on a hand towel

Abstract

To determine whether a DNA type can be detected from a touch sample, we established a scenario imitating a crime in which an assailant attempted to push a hand towel into the victim’s mouth. Skin secretion from the assailant and saliva from the victim were assumed to be attached to the towel. These towels potentially contained a mixture of cells from skin and saliva with a low copy number (LCN). Extracted DNA was used as a template for DNA analysis using AmpFlSTR Identifiler Plus Kit (Thermo Fisher), mtDNA (D-loop) sequencing using Dye Terminator v3.1 Cycle Sequencing Kit (Thermo Fisher), and MPS sequencing using the MiSeq FGx System (Verogen). The results showed that a mixed profile of the assailant and the victim was obtained from four samples, while a single profile of the assailant was obtained from six samples out of ten using each of the above three methods. Regarding these three methods, their detection power was approximately equivalent and extremely high; the SNP method by FGx is the most sensitive and reliable for the analysis of mixed samples.