Raoul Wallenberg was the diplomat who would appear like a phantom in Budapest, handing out the Swedish passports that saved some 15,000 Hungarian Jews from being murdered by the Nazis. But Wallenberg had no such help himself on January 17, 1945, when he was taken into custody by the Soviet forces that had liberated Budapest. The Swedish diplomat was never heard from again, and Moscow would later report that Wallenberg had died in Lubyanka Prison in 1947.

But in the 63 years since his arrest, the Wallenberg family and generations of researchers have relentlessly pursued the possibility that the Swedish diplomat survived long after 1947, as a secret prisoner in the Soviet gulag system. "There are plenty of indications that he may have survived past 1947, and these deserve thorough examination," says Susanne Berger, a German-born researcher who has spent 15 years exploring Wallenberg's fate.

Skeptics ask what motive the Soviets might have had for imprisoning Wallenberg, and for lying about his fate for decades after. Scholars exploring Wallenberg's relationship with the intelligence agencies battling each other in wartime and postwar Hungary, however, suggest that Moscow may have perceived the Swede as a spy for the West.