Complex DNA mixture analysis: Report of two cases

Abstract

During the last years, DNA profiling techniques have become more sensitive and mixtures with multiple contributors occur often. Nevertheless, interpretation of mixture profiles is the most complex task in the forensic field. The ISFG published recommendations for the interpretation of mixed DNA profiles that may have allelic drop-out or drop-in. The DNA commission of the ISFG has supported the use of likelihood ratios (LRs) as preferable to other methods. LR can be calculated by probabilistic programs, using semi and fully continuous (probabilistic) methods. These methods increase the efficiency of forensic laboratories and improve the consistency and transparency of the reported results. LRmix is an open-source system dedicated to the interpretation of forensic DNA profiles with a particular focus on complex DNA mixtures. This software is programmed on a LR model and facilitates the calculation of LR for complex mixtures, with partial profiles with known and unknown contributors. Here, we report the re-analysis of two old complex cases processed in our laboratory in the last years. In both cases, we used the software LRmix Studio with interesting consequences: in one case we solved the crime, in the other one, the results allowed the case to be reopened.