The two victims did not know each other, and police found no connection between them and their killer. The seemingly random nature of the attacks terrified the city. The investigation that followed became Sweden’s second-largest in history, surpassed only by the 1986 assassination of Prime Minister Olof Palme.
Investigators collected DNA evidence from a bloody beanie cap and the murder weapon left at the scene. Over the years that followed, they conducted 7,000 interviews, received 13,000 tips, and gathered 5,000 DNA samples — without ever finding a match. The case went cold and stayed that way for 16 years.
Forensic genetic genealogy: a European first that solved the case in 5 weeks
In 2020, genealogist Peter Sjölund — one of the co-authors of the 2021 book on which the series is based — introduced a new DNA analysis method to Swedish police. The technique combined forensic DNA evidence with genealogical research to identify distant relatives of an unknown suspect.
Investigators uploaded the killer’s DNA profile to databases including GEDmatch and FamilyTreeDNA, comparing it against hundreds of thousands of genetic markers voluntarily shared by members of the public. Sjölund then traced the DNA back 200 years through church registers, death notices, and genealogical records.
Within 5 weeks, he had constructed a family tree that pointed to two brothers as potential suspects. It marked the first time in European history that a murder case was solved using genetic genealogy. The technique had previously been used in the United States to identify the Golden State Killer, Joseph James DeAngelo, in April 2018.
Forensic genetic genealogy: from California to Linköping
The technique used to solve the Linköping case was pioneered in the United States, where it helped identify the Golden State Killer, Joseph James DeAngelo, in April 2018. It works by matching crime scene DNA against genetic markers voluntarily uploaded to genealogy databases, then building family trees to narrow down suspects. Sweden became one of the first European countries to legislate for its use, amending its laws in January 2019.
