Forensic casework of personal identification using a mixture of body fluids from more than one person by Y-STRs analysis

We applied Y-STRs (DYS385/DYS19/YCAII) to an adhesive plaster left at a crime scene. This plaster may have included body fluids from more than one person. Firstly, we performed preliminary examinations, ABO-blood type examinations, and commonly used DNA examinations (D1S80, HLADQα, TH01, and PM) on these specimens. As a result of these examinations, we could evidence that suspect A did not contacted with the plaster, but could not confirm the presence of perspiration from suspect B. As the next step, we applied Y-STR examination to the plaster. Using this examination, we detected alleles that coincided to those of suspect B. We also concluded that the fluid from an unidentified person was vaginal fluid based on crime scene investigation. Y-STRs examination data obtained from 124 persons in Tokushima prefecture showed that 1.613% of individuals demonstrated haplotypes 10-18/ 15/19-23, which was detected from the plaster and from suspect B. Therefore, we considered that there was a high probability that the persiration detected in the plaster was that of suspect B. Based on these studies, we concluded that Y-STR examination of trace evidence was very useful to screen suspects using materials that contained body fluid from more than one person.