Swedish police said they would test a gun that may shed new light on the unsolved 1986 assassination of former Prime Minister Olof Palme, describing it as one of the best leads they have had for almost 20 years.
However, a state prosecutor played down the idea that it would solve the mystery of who shot the prime minister. Palme was shot in central Stockholm after going to the cinema with his wife. A man was jailed for the crime, but later released on appeal.
The murder weapon was never found.
Now divers hired by tabloid newspaper Expressenhave discovered in a lake a gun police have sought for two decades as the only one known to have fired ammunition from the same batch as the bullet that killed Palme .
"This means that we have now found a weapon to which we have given a highest priority," Stig Edqvist, head of the police's Palme investigation unit, told reporters.
"We have spent a lot of resources trying to find it."
Agneta Blidberg, the state prosecutor working on the case, told Swedish news agency TT her hopes were not high.
"The likelihood that we have found the murder weapon is not particularly great," she said.
The last known use of the gun found in the lake was in a robbery in 1983. Police were told it had been thrown into a lake shortly afterward, but they had never been able to confirm this.
If it is the Palme murder weapon, it was either never dumped in the lake in 1983 or was fished out and then thrown back.
The police will also focus attention on the bullets in the gun, which could have been taken out of the weapon before it was thrown in the lake and subsequently used in the Palme killing.
The lead, despite being slim, is one of the best in the case since the overturning in 1989 of the conviction of petty criminal Christer Pettersson. He died two years ago.
The mystery has prompted several false leads over the years. In March this year a man handed over a revolver barrel to police, who later said it was not part of the murder weapon.