Prosecutors based part of these allegations on an ID card referred to as the "Trawniki card". Because the Soviet Union generally refused to cooperate with the Israeli prosecutions, this ID card was obtained from the USSR and provided to Israel by American industrialist Armand Hammer, a close associate of several Kremlin leaders, whose help had been requested by the personal appeal of Israeli president Shimon Peres. The defense claimed that the card was forged by Soviet authorities to discredit Demjanjuk. The card had Demjanjuk's photograph, which he identified as his picture at the time. The prosecution called expert witnesses to testify on the authenticity of the card including its signatures by various Nazi officers, paper, and ink. The defense used some evidence supplied by the Soviets to support their case while calling other pieces of evidence supplied by the Soviets "forgeries".