Beyond Direct Contact: Secondary Transfer of Touch DNA and Its Implications for Forensic Interpretation

The secondary transfer of touch DNA has become a significant issue in contemporary forensic science due to advances in DNA profiling methods. Touch DNA involves genetic material left behind through the shedding of epithelial cells during physical contact, allowing for the extraction of DNA profiles from very small biological samples. In the past, finding an individual’s DNA on an object was seen as proof of direct interaction; however, recent studies have revealed that DNA can also be transferred indirectly via intermediary people or objects. This occurrence challenges the traditional understanding of DNA evidence and prompts crucial inquiries about the connection between DNA detection and actual participation in a criminal act. This review highlights the current knowledge regarding secondary transfer mechanisms, the various factors that affect its occurrence, and findings from experimental studies performed in both controlled and realistic settings. The variability linked to shedding ability, contact conditions, surface characteristics, and environmental influences underscores the unpredictable nature of indirect DNA transfer. Additionally, the review examines how secondary transfer impacts forensic interpretation, stressing the importance of shifting from a source-level to an activity-level assessment. Grasping the limitations and possible alternative transfer scenarios is crucial for precise evidence interpretation, effective courtroom communication, and the responsible use of touch DNA analysis in forensic practice.