Associative DNA sampling on clothing is commonly used in forensic casework to identify the individual who may have worn an item. Once a DNA profile is obtained, questions arise about whether it originated from the most recent wearer, the habitual wearer, or through indirect DNA transfer. This study used STRmix™ to deconvolute mixture profiles from known habitual and recent wearers, examining trends in DNA profiles from various clothing items, sampling locations, methods, and fabric types. The study included six clothing items worn by ten volunteer pairs to simulate real-life wear. Items included athletic tops, t-shirts, gloves, hats, sweatpants, and sweatshirts. Cutouts and swabs were taken from each item, with multiple locations sampled for sweatpants and sweatshirts. Athletic tops (polyester) and t-shirts (cotton), worn for one day by each pair, showed nearly equal DNA profile contributions from the habitual and recent wearers, suggesting that fabric type does not significantly affect DNA deposition. For other items, the habitual wearer was Contributor 1 in 99/133 samples and Contributor 2 in 8/133, the recent wearer was Contributor 1 in 7/133 and Contributor 2 in 60/133, and non-wearer DNA was Contributor 1 in 1/133 and Contributor 2 in 29/133. Equal profile contributions were found in 26/133 samples. In all samples, 75/172 had non-wearer DNA. No significant differences were found in profile contributions across sampling locations or between cutouts and swabs for each item. Glove samples had the highest quantitation results, while sweatpants pockets had the lowest. Quantitation results showed no major difference between cutouts and swabs for most items, except athletic tops (swabs > cutouts) and sweatshirt cuffs (cutouts > swabs). No significant difference was observed between athletic tops and t-shirts. These findings can help forensic scientists address activity level propositions for clothing evidence and assist forensic labs in developing protocols for effective clothing sampling strategies for obtaining high-quality DNA profiles suitable for CODIS upload.

Authors

• Renata Dziak (Centre of Forensic Sciences, Canada)
• Stacey Sainte-Marie (Ontario Tech University, Canada)
• Kimberley Nugent (Ontario Tech University, Canada)
• Sonja Stadler (Centre of Forensic Sciences, Canada)
• Kaitlyn Corrigan (Ontario Tech University, Canada)
• Natalia Robinson (Ontario Tech University, Canada)
• Roxanne Kerr (Ontario Tech University, Canada)
• Tristan Rajanayagam (Ontario Tech University, Canada)