Establishing a baseline for background and purchaser DNA in new unwashed underwear for the purpose of evaluative reporting

Abstract

This study was designed to establish a baseline of both background deoxyribonucleic acid (DNA) from unknown sources and purchaser DNA that may be recovered from new unwashed children’s and adult’s underwear. Fourteen children’s underwear and 10 adult’s underwear items were tested. Despite no male donors being utilized for the study, male DNA was detected on 17 out of 24 of the samples, demonstrating that the presence of an unknown donor’s DNA on new, unwashed, unworn underwear should be expected on most samples. Four samples (16.7%) were deemed suitable for comparison based on the laboratory’s thresholds for comparison. Of the four samples deemed suitable, three resulted in inclusionary likelihood ratios (LR) for the donor that briefly handled the underwear, i.e. the purchaser. The percent portion of the assigned LR contributor position associated with the purchaser did not exceed 61.0%. This research suggests that very limited and transient contact with new underwear has resulted in DNA transfer sufficient for comparison, providing evidence that this level of contribution should be considered in analysis and interpretation when evaluating DNA profiles obtained from newly purchased, unwashed underwear.