A genealogy expert and DNA helped Swedish police solve a 16-year-old double-murder, in a case that is due to go trial later this month.
A man was charged on Wednesday for the 2004 murders of an 8-year-old boy and a 56-year-old woman in the city of Linkoping, near Stockholm, the prosecutor said.
The victims were stabbed, triggering a lengthy and extensive investigation.
"Everything suggests these were two random victims and we have not found any connection between him and the victims," prosecutor Britt-Louise Viklund said of the suspect.
The man was arrested in June and admitted to the crimes during questioning.
He lived quietly in Linkoping and managed to elude eluded the police, even though a knife, cap and fingerprints were found at the scene. The woman had also described her assailant before she died.
DNA of 5,000 people tested
During their investigation, police conducted several thousand interviews and tested the DNA of 5,000 people.
A breakthrough came earlier this year when DNA from the crime scene was uploaded to a commercial website in the US that sells DNA tests to hobby genealogists.
Using the matches, Swedish genealogist Peter Sjolund helped police create family trees back to the 18th century. He narrowed the search down to two brothers, and the younger of the two was then arrested.
Viklund said she had not been able to establish a motive other than that the accused told police he had "a picture inside him that he interpreted as telling him to kill two people."
If convicted, experts may find the accused has diminished capacities, in which case he could be committed to a psychiatric hospital.