A crime case involving a mixture of three individuals solved using a sample from the daughter of the person of interest

A forensic genetics laboratory may well receive requests that are out of the ordinary and pose challenges like the one presented in this case. A mixture from three individuals was analysed from a crime scene. Reference samples were obtained from two individuals. The Person Of Interest (POI) was not available, only a putative daughter. The analysis of Y and X-STR markers indicated that the contributors to the bloodstain mixture were two males and one female. The hypotheses for the calculation of the Likelihood Ratio (LR) were specified and evaluated using autosomal STR markers. The calculations were done using the open and freely available programs relMix and EuroFormix. The software relMix can deal with arbitrary family relationships between contributors while EuroFormix only accommodates pairwise relationships. In this case both programs were applicable. EuroFormix models peak heights resulting in higher LR, as expected. Ultimately, results from both programs identified the POI, leading to the resolution of the case.