Getting the conclusive lead with investigative genetic genealogy - A successful case study of a 16 year old double murder in Sweden

Abstract

On the morning of October 19, 2004, an eight-year-old boy and a 56-year-old woman were stabbed to death on an open street in the city of Linköping, Sweden. The perpetrator left his DNA at the crime scene, and after 15 years of various investigation efforts, including more than 9000 interrogations and mass DNA screening of more than 6000 men, there were still no clues about the identity of the unknown murderer. The successful application of investigative genetic genealogy (IGG) in the US raised the interest for this tool within the Swedish Police Authority. After legal consultations it was decided that IGG could be applied in this double murder case as a pilot case study. From extensive DNA analysis, including whole-genome sequencing and genotype imputation, DNA data sets were established and searched within both GEDmatch and FamilyTree DNA genealogy databases. A number of fairly distant relatives were found from which family trees were created. The genealogy work resulted in two candidates, two brothers, one of whom matched the crime scene samples by routine STR profiling. The suspect confessed the murders at the initial police hearing and was later convicted of the murders. In this paper we describe the successful application of an emerging technology. We disclose details of the DNA analyses which, due to the poor quality and low quantity of the DNA, required reiterative sequencing and genotype imputation efforts. The successful application of IGG in this double murder case exemplifies its applicability not only in the US but also in Europe. The pressure is now high on the involved authorities to establish IGG as a tool for cold case criminal investigations and for missing person identifications. There is, however, a continuous need to accommodate legal, social and ethical aspects as well.

Keywords: Forensic DNA; Forensic genetic genealogy (FGG); Genotype imputation; Investigative genetic genealogy (IGG); Whole genome sequencing.