Judges at the trial of alleged Nazi war criminal John Demjanjuk barred the defense from trying to discredit U.S. industrialist Armand Hammer, who helped provide a key piece of evidence against the accused. The court barred a defense witness, historian Nikolai Tolstoy of Britain, from answering when defense attorney Yoram Sheftel asked him whether he believed Hammer was part of a plot against the Ukrainian-born Demjanjuk. "We will not hear any words against Hammer in this courtroom," Chief Justice Don Levin said. Hammer helped Israel obtain from the Soviet Union a Nazi identity card that prosecutors say was issued to Demjanjuk during World War II. The defense says the card is a Soviet forgery.