Larsson, who died in 2004, drew up a will in 1977 before a trip to Ethiopia, which was in civil war at the time, according to Sveriges Television's investigative news program Uppdrag Granskning.
He was 22-year-old struggling author at the time, but still took the time to spell out how his meager inheritance should be distributed.
“I am hardly a rich man, but I want that my monetary assets to go to the Communist Workers Party's Umeå chapter,” wrote Larsson.
However, the will has no witnesses.
Larsson's books, the Millennium-trilogy, have generated millions. According to the program, the author, were he alive today, would have earned close to 80 million kronor ($13.3 million) from the three published books.
After his death, all of Larsson's assets went to his father and brother. His partner Eva Gabrielsson didn't inherit anything, which has led to a painful dispute, especially when it comes to how Larsson's literary works are administered.
According to Uppdrag Granskning there is “nearly finished material” for a fourth book in the series about the computer hacker Lisbeth Salander and journalist Mikael Blomkvist.
The dispute between Gabrielsson and Larsson's father and brother has yet to be settled.