Crime writer Stieg Larsson turned detective and tried to help cops crack the notorious murder of Swedish Prime Minister Olof Palme.

The author, who penned the Millennium trilogy of novels including hit book The Girl with the Dragon Tattoo, was fascinated by the 1986 killing and spent almost a year investigating the case with his ex-girlfriend Eva Gabrielsson.

He later gave police the name of a man he suspected of involvement in the shooting, but although the suspect was spoken to by officers, he was never formally accused.

Details of Larsson's probe emerged in 15 boxes of material on the killing which was collected by the author prior to his death in 2004.