This multi-site study aims to compare the performance of both swab and tape collection tools across three ISO/IEC 17025 accredited forensic DNA laboratories from Switzerland and France, each using different routine DNA analysis methods. 

For this purpose, Copan Forensic 4N6FLOQSwab™ and Coloprint DNA-tape™ were compared in terms of DNA recovery efficiency and DNA profile quality. Mock trace samples were generated by simulating an assault scenario between two persons, in which one person pushed the other in the back for approximately 10 seconds. To allow direct comparison, traces deposited by the volunteers’ dominant and non-dominant hands were alternately collected using swabbing and tapping. 30 volunteers per laboratory were recruited, resulting in a total of 90 volunteers providing 180 traces recovered on clothing for analysis. 

To assess potential differences between the two collection methods, three metrics were considered: DNA quantity, eligibility for CODIS submission (i.e. single source or major component), and eligibility for DBLR submission (i.e. including DNA mixtures). DNA quantities were compared using Bayesian statistics. DNA profiles were further analyzed using the probabilistic genotyping software STRmix™, with genotype weights serving as criteria for CODIS submission eligibility. To establish the weight threshold required for CODIS submission eligibility, multiple thresholds between 70% and 99% were assessed against ground truth data. For DBLR submission we used an LR threshold of 10⁶.

Furthermore, this study generates reference data to support evaluations given activity-level propositions by establishing baseline expectations for DNA recovery from clothing in the context of assaults (i.e., pushing in the back).

Authors

• Séverine Nozownik (Unit of Forensic Genetics, University Center of Legal Medicine, Lausanne - Geneva, Lausanne University Hospital and University of Lausanne, Switzerland)
• Venus Kallupurackal (Department of Forensic Genetics, Zurich Institute of Forensic Medicine, University of Zurich, Switzerland)
• Chloé Scherer (Institut de Recherche Criminelle de La Gendarmerie Nationale, France)
• Patrick Basset (Unit of Forensic Genetics, University Center of Legal Medicine, Lausanne - Geneva, Lausanne University Hospital and University of Lausanne, Switzerland)
• Tacha Hicks (Unit of Forensic Genetics, University Center of Legal Medicine, Lausanne - Geneva, Lausanne University Hospital and University of Lausanne, Switzerland)
• Francis Hermitte (Institut de Recherche Criminelle de La Gendarmerie Nationale, France)
• Cordula Haas (Department of Forensic Genetics, Zurich Institute of Forensic Medicine, University of Zurich, Switzerland)
• Vincent Castella (Unit of Forensic Genetics, University Center of Legal Medicine, Lausanne - Geneva, Lausanne University Hospital and University of Lausanne, Switzerland)