By Adam Easton
BBC News, Warsaw
The general was the leader of Poland's government-in-exile
Investigators in Poland say there is no evidence to back up theories that the country's wartime leader, General Wladyslaw Sikorski, was murdered.
The general died when his plane crashed off Gibraltar in 1943, but some of the details of the crash remain unclear.
This has fuelled some people's belief that he may have been killed by the Soviet Union or Britain.
Two months ago, the Polish authorities exhumed the general's body in a bid to clear up the mystery.
But the results of their medical tests have dealt a severe - if not quite fatal - blow to the theory that Gen Sikorski was murdered.
The investigation found that Poland's wartime hero, who led its government-in-exile, died as a result of multiple organ failure of the kind typically sustained in a plane crash.
It found no evidence that he was poisoned, shot or strangled.
But the institute which investigates World War II-era crimes said it would continue to probe whether sabotage caused the general's Liberator bomber to crash seconds after it took off from Gibraltar.
A British investigation at the time found that the plane crashed for unknown reasons, perhaps because its controls had jammed.
Over the years historians and even playwrights have speculated that Gen Sikorski was murdered on the orders of Joseph Stalin or British Prime Minister Winston Churchill to prevent a split between the allies.
Shortly before he died, Gen Sikorski had demanded an investigation into the discovery of the bodies of thousands of Polish officers in mass graves in forests near Katyn in the former Soviet Union.