A case of contamination by indirect DNA transfer in a sexual assault case: A taste of déjà vu?

In this article, we explore, through a casework example, when it is both appropriate and beneficial to provide possible explanations for contradictory information in a forensic context. We demonstrate that the challenges faced in forensic genetics are similar to those described decades ago in disciplines dealing with trace materials, such as fibres. This case, involving a DNA contamination within police premises by a blanket used by the two persons involved, serves as a reminder that all key players involved at the scene or working with complainants and defendants must remain vigilant in minimizing undesirable transfers of DNA or other traces. We show that rather than working in silos, DNA scientists should capitalise on the knowledge that has been acquired in other forensic disciplines. Based on Best Practice Manuals from several disciplines, we suggest general recommendations to prevent contaminations that can be potentially incriminating. Additionally, this case highlights the importance for members of the judiciary to recognize that all forensic results (e.g., fibres, DNA, mobile phone records), regardless of their strength, must be assessed within the broader context of the case, considering all available evidence rather than relying on a single forensic element.