2004–2005 GEP proficiency testing programs: Special emphasis on the interlaboratory analysis of mixed stains

Abstract The 2004–2005 GEP proficiency testing programs consisted of a simulated paternity case and a simulated forensic criminal case each including 3–5 reference samples (saliva or blood) and 2 forensic samples (mixed stains and clean or contaminated hair shafts). In the 2004 forensic test a mixture stain was analysed and apparently inconsistent results were observed between autosomal STR profiling and mitochondrial DNA sequencing results. In 2005, the forensic challenge was an unbalanced mixture stain of saliva and blood from two related contributors (sharing maternal and paternal lineages). Due to the stain characteristics, no lab detected the minor component in the mixture. This evidences the fact that the detection of a minor contributor in a mixture is still a key outstanding in forensic investigation. Also hair shafts contaminated with blood have been sent to be analysed and the results showed the influence of the extraction procedures applied.