Genetic/epigenetic DNA markers for linking suspects and tissues in complex crime scenes

Analysis of DNA found at a crime scene can provide crucial information on the identity of the individual who has left the DNA, as well as the tissue origin of the DNA. However, the current methods used for DNA profiling and for the identification of cellular origin are separated—they do not associate genetic profiles found in the DNA evidence with epigenetic information about the biological origins of that same DNA. In this study, we developed a method based on joint genetic/epigenetic analysis of the same DNA molecule, allowing us to concurrently identify both the donor and the cellular origin at a single DNA molecule resolution. For this, we created a forensic body fluid methylation atlas, containing blood, semen, skin, and urine, and identified 800 tissue-specific methylation markers. Of these, nearly one hundred markers capture genetic information of nearby single nucleotide polymorphisms. We sequenced and tested 53 of these markers, including 12 for blood, 12 for skin, 14 for semen, and 15 for urine, in a joint genetic/epigenetic analysis. This allowed us to associate specific DNA fragments to their origin, by concurrently identifying their body fluid or tissue type and donor. Using our method, it is possible to disentangle complex crime scenes, composed of mixed biological materials and donors, and identify which donor contributed which tissue type. The method will allow forensics laboratories around the world to better understand the origin of DNA mixtures found at complex crime scenes, and help to check the testimonies of parties involved in criminal cases.