an excerpt from
http://en.wikipedia.org/wiki/Ivan_the_Terrible_(Treblinka_guard) :
Ivan the Terrible (born c. 1911) is the nickname given to a notorious guard Ivan Marchenko, at the Treblinka extermination camp during the Holocaust.[1] The moniker alluded to Ivan IV, also known as Ivan the Terrible, the infamous Tsar of Russia. "Ivan the Terrible" gained international recognition from the 1986 John Demjanjuk case; however very little is known about Ivan Marchenko, and he is not mentioned in any early authoritative Holocaust literature. John Demjanjuk was accused first of being Ivan the Terrible at the Treblinka concentration camp, but in 2011 he was accused of war crimes as a different guard named Ivan Demjanjuk who served at the Sobibor extermination camp.
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Ivan's true identity has not been conclusively discovered, however, throughout the 1970s and eighties John Demjanjuk, a retired suburban Cleveland autoworker of Ukrainian descent, was accused of being Ivan.[1] He was tried in Israel in 1986 and sentenced to death, but the conviction was overturned due to lack of evidence.[14][15]
One remarkable event, during the Israel trial, involved a star witness for the prosecution, Eliyahu Rosenberg. Asked by the prosecution if he recognized Demjanjuk, Rosenberg asked Demjanjuk to remove his glasses "so I can see his eyes." Rosenberg approached and peered closely at Demjanjuk's face. When Demjanjuk smiled and offered his hand, Rosenberg recoiled and shouted "Grozny!" meaning "Terrible" in Polish and Russian. "Ivan," Rosenberg said. "I say it unhesitatingly, without the slightest shadow of a doubt. It is Ivan from Treblinka, from the gas chambers, the man I am looking at now." "I saw his eyes, I saw those murderous eyes," Rosenberg told the court, glaring at Demjanjuk. Rosenberg then exclaimed directly to Demjanjuk: "How dare you put out your hand, murderer that you are!"[16] It was later revealed with great embarrassment for the prosecution, that Eliyahu Rosenberg had previously testified in a 1947 deposition that “Ivan the Terrible” had been killed during a prisoner uprising.[17]