Philipp von Boeselager, a German army officer, said he obtained for the other plotters the explosive that was detonated under a table at Hitler's Wolf's Lair headquarters in present-day Poland on July 20, 1944.
A feature film about the plot, starring Tom Cruise as Colonel Claus von Stauffenberg, who planted the bomb, is set for release next year.
Baron von Boeselager said he escaped being caught because none of the captured conspirators had revealed his name under torture.
