The gun used in a 1983 robbery in the small town of Mockfjärd was finally found and handed over to the police on Monday.
The special investigative unit charged with unravelling the Palme murder mystery has long considered this particular revolver one of the most likely murder weapons.
In 1997 police spoke to Pekka, 57, who drove the getaway car from Mockfjärd in 1983.
Pekka spent time behind bars in the high security Kumla prison in 1982. At that time Christer Pettersson was also holed up in Kumla. Pekka claims to have come into contact with the man whose name later became synonymous with the Palme murder investigation.
One of the Mockfjärd robbers told police he had thrown the revolver into a lake called Flosjön in 1983. But Expressen's divers eventually found the weapon this week in a different lake, known as Djursjön.
According to Pekka's version of the story, he sold the weapon to Christer Petterson in 1985, one year before the murder of Olof Palme in central Stockholm.
“The big question now is whether the revolver has been lying in the water since the 1983 robbery, or whether it was used after that,” former chief investigator Lars Nylén told Expressen.
The main priority for police now is to restore the revolver to a point where it becomes usable. The weapon has been sent to the National Laboratory of Forensic Science, where experts are attempting to stop the rusting process and make it possible to fire test shots.
“We want to look at the bullets and compare them with bullets from the Olof Palme crime scene,” Sabine Rütten, spokeswoman for the National Laboratory of Forensic Science, told The Local.
“Firing a shot from a weapon provides useful details. When a shot is fired it passes through the barrel and leaves marks on the bullet which can be compared with other bullets fired from the same gun,” said Rütten.