Recent advances in the sensitivity and precision of forensic DNA analytic methods - alongside with to the more frequent use of probabilistic evaluation - now allow (partial) DNA profiles to be reliably assigned to one or more individuals, even when the trace material has been compromised by age, environmental conditions, and/or contamination. Individualization is now routinely achieved with minute amounts of biological material. Consequently, the focus of interest in trace interpretation in forensic molecular biology has shifted: the contextualization of and in particular to answer the question how and when a trace had been deposited has become significantly more important for the forensic interpretation of DNA findings. In this manner, research on the interpretation of traces given activity-level propositions and DNA transfer, persistence, prevalence, and recovery (TPPR) has grown in impact and importance.

Here, we introduce "TransAct", a collaborative multi-laboratory initiative designed to rationalize research into and data collection form forensic nucleic acid transfer. Variables that affect DNA-TPPR were assessed by conducting highly standardized experiments performed by eight collaborating forensic laboratories. Initial results reveal pronounced variability in DNA recovery among participating labs using their routinely used standardized casework protocols, with yields varying by orders of magnitude. Significant discrepancies were observed between different qPCR systems, as well as substrate-dependent differences in DNA persistence. These findings underscore that TPPR data are profoundly influenced by laboratory-specific methodological differences, emphasizing the critical need for experimental standardization and shared resources to enhance the reliability of nucleic acid TPPR research and thereby improving activity level evaluation in forensic genetics.

Authors

• Kathrin Broderius (Institute of Legal Medicine, University Hospital of Cologne, Germany)
• Felix Fries (Institute of Legal Medicine, University Hospital of Cologne, Germany)
• Galina Kulstein (Federal Criminal Police Office (Bundeskriminalamt), Germany)
• Iris Buckel (Federal Criminal Police Office (Bundeskriminalamt), Germany)
• Oliver Krebs (Institute of Legal Medicine, University Medical Center Hamburg-Eppendorf, Germany)
• Christa Augustin (Institute of Legal Medicine, University Medical Center Hamburg-Eppendorf, Germany)
• Theresa Siekmann (LABCON-OWL Analytik, Forschung und Consulting GmbH, Germany)
• Helena Siemens (LABCON-OWL Analytik, Forschung und Consulting GmbH, Germany)
• Janine Silvery (LABCON-OWL Analytik, Forschung und Consulting GmbH, Germany)
• Eva Schnitzler (State Criminal Police Office (Landeskriminalamt) Rhineland-Palatinate, Germany)
• Stefanie Grethe (State Criminal Police Office (Landeskriminalamt) Rhineland-Palatinate, Germany)
• Emelie Hanf (Institute of Legal Medicine, University Hospital of Ulm, Germany)
• Malte Bamberg (Institute of Legal Medicine, University Hospital of Ulm, Germany)
• Venus Kallupurackal (Zurich Institute of Forensic Medicine, University of Zurich, Switzerland)
• Cordula Haas (Zurich Institute of Forensic Medicine, University of Zurich, Switzerland)
• Kristina Schulze-Johann (Institute of Legal Medicine, University Hospital of Münster, Germany)
• Marielle Vennemann (Institute of Legal Medicine, University Hospital of Münster, Germany)
• Cornelius Courts (Institute of Legal Medicine, University Hospital of Cologne, Germany)