Casework-related DNA transfer on footwear in consideration of the shedder status

DNA evidence on shoes can play an important role in solving a variety of crimes. We investigated the transfer, persistence, prevalence and recovery of DNA (DNAtppr) on shoes (sneakers) and their soles in realistic handling scenarios taking into account the shedder status. This study aims to increase the understanding of the expected composition of DNA profiles and their probative value, providing a basis for activity level assessments. Samples were analyzed using a direct lysis method, suggesting its versatility and increasing the DNA typing success compared to previous studies on footwear. The data showed surface-dependent background DNA (bDNA) levels on shoe soles and prevalence of bDNA on the upper parts of the shoe. The owner of the shoe was allocatable to the mixture for almost every shoe and sampling location. Alternating scenarios of shoe handling were simulated through different pairs of shedders to distinguish shoe owner and subsequent user. Secondary users were attributable to DNA mixtures regardless of shedder status after wearing shoes a single time. The influence of the shedder status follows specific trends in this context. However, particularly intermediate shedders show inconsistent results. The prevalence of bDNA appears to have a greater effect on the impact of the shedder status on DNA profile composition than previously reported. The data help researchers to better resolve suspect statements and determine if a person of interest wore the shoes relevant to the investigation.