STOCKHOLM — A newly found Swedish document shows how the KGB intervened in the early 1990s to stop an investigation into World War II hero Raoul Wallenberg's fate, two U.S.-based researchers said Monday.

The Swedish diplomat, who would have turned 100 this year, is credited with rescuing tens of thousands of Hungarian Jews from the Nazis. He disappeared after being arrested in Hungary by the Soviet Red Army in 1945.

The Russians have said he was executed on July 17, 1947, but unverified witness accounts and newly uncovered evidence suggest he may have lived beyond that date.

Wallenberg researchers were hoping that key pieces of the puzzle would emerge when an international commission was granted access to Soviet prison records as the communist rule was heading toward its end....