"I go there in my dreams. They are so real. In them I am still there," said Thomas Blatt, 82, whose parents and brother were among the 250,000 people estimated to have perished there during World War II.
"I can't get it out of my head. This is the price I paid for getting out." He told the court in Munich that he was unable to place Demjanjuk, 89, at the camp in occupied Poland, but that "only Ukrainians like Mr. Demjanjuk guarded us".
"The Ukrainians were always there, they were the most important personnel in Sobibor," Blatt said. "Without them, the death factory wouldn't have functioned ... The Trawnikis (foreign guards) were worse than the Germans."
"Lots of Ukrainians ran away, they were able to run away ... He (Demjanjuk) was free to go. I had a death sentence."
Ukrainian-born Demjanjuk was deported from the United States last May and has been on trial since November 30, accused of being an accessory to the murder of 27,900 Jews during his alleged time at Sobibor in 1943.
There are no living witnesses able to positively identify Demjanjuk, but the prosecution says it has an SS identity card proving he was at the Trawniki training camp for guards and that he was transferred to Sobibor.
Prosecution lawyers are using testimony from survivors to prove that if Demjanjuk was a guard at the camp, then he would have played an active role in the mass killing that took place.
"It was 65 years ago. That is a long time. My memory isn't that good now," said German-born Blatt, who now lives in California, but that he remembered being faced with death "every second". "I can't remember my mother's face any more, or my father's."
Demjanjuk, whose family says he is gravely ill and who again appeared in court on a stretcher Tuesday, denies the charges but has so far declined to address the court. The trial, likely to be the last major case dealing with war crimes during the Nazi regime, is due to last until at least May.