MUNICH — Ukrainians who served under the SS at the Nazis' Sobibor death camp were instrumental to the killing of Jews, a survivor testified Tuesday at the trial of John Demjanjuk, who is accused of being a guard there.

Witness Thomas Blatt, 82, told the Munich state court he didn't remember the Ukrainian-born Demjanjuk from Sobibor, but said that if his presence could be proven he must have been involved in Jews' extermination.

Demjanjuk, an 89-year-old retired Ohio auto worker, was deported from the U.S. last year for the trial in Germany. He is charged with 27,900 counts of accessory to murder for his alleged activities as a guard at Sobibor, in occupied Poland, in 1943.

Blatt said that, more than six decades later, he doesn't even remember the faces of his mother and father, who were killed in Sobibor.

"I can't say if Demjanjuk was at Sobibor," the white-haired Blatt said, alternating between broken German and accented English.

"But I know that this group of Ukrainians were a very important part in the extermination of the Jews. If Demjanjuk was at Sobibor, he was a murderer."

Demjanjuk, once a Soviet Red Army soldier, is accused of agreeing to serve as a guard for the SS and training at the Nazis' Trawniki camp following his capture in 1942.

Demjanjuk maintains he was never at the camp and questions the authenticity of a key piece of evidence — an SS identity card that prosecutors say features a photo of a young Demjanjuk and that says he worked at Sobibor.

"It is no surprise the former Sobibor laborers do not know him now and could not identify him at any time prior because he was not there," his son, John Demjanjuk Jr., said in an e-mail to The AP after the session.

Demjanjuk himself showed no reaction to the testimony, lying on a bed with a pillow propping up his head and a baseball cap over his face. After the proceedings, however, he seemed alert as guards wheeled him away.

Blatt, who today lives in California, told the court there were about 150 Ukrainian guards at Sobibor, who served under the supervision of about 15 German SS men at any given time.

He identified many SS men by name and rank, but said he only remembered the names of two of the Ukrainians and "did not have a lot of contact with the watchmen."

But, he said, the Ukrainian guards were instrumental in keeping prisoners from fleeing while on work details outside the camp.

"There was no fence in the forest," Blatt testified. "We had only the Ukrainians like Mr. Demjanjuk to keep us from fleeing."

Demjanjuk's defense attorney Ulrich Busch questioned the value of Blatt's testimony — saying that not only could he not identify his client, "his memory is not precise any more."

"It's ridiculous — he tries to acquit Germany and convict the Ukrainians and other Eastern Europeans of responsibility for the Holocaust," Busch said after the court session. If the Ukrainians "did something, they did so because they were commanded by the Germans."

Though Demjanjuk's defense maintains he was never at Sobibor, Busch has also argued that the Ukrainian guards used by the Nazis agreed to serve only to escape likely death in POW camps, and that they would have been killed if they didn't follow orders.

Blatt, who has joined the trial as a co-plaintiff as allowed under German law, is one of only 66 Sobibor prisoners believed to have survived the war.

His mother, father and brother were killed immediately after the family was deported to the Sobibor camp from their town in Poland in April 1943. Blatt was spared because he was selected to work in the camp.

Blatt said Polish Jews who lived near the camp knew what awaited them, but those arriving from other parts of Europe had no clue.

He pointed out a building where he worked cutting the hair of female prisoners after their arrival — before they were sent into the gas chambers, which they were told were a disinfectant shower.

"The women from Holland, they didn't know they were going to their deaths," he recalled. "They said: 'Please don't cut it so short,' but the Poles knew. They said: "Why are you doing this?'"

Blatt testified that, because of what the Polish Jews knew, they did not go into the gas chambers willingly.

"The Ukrainian guards forced them into the gas chambers with bayonets," he testified.

Demjanjuk had his U.S. citizenship revoked in 1981 after the Justice Department alleged he hid his past as the notorious Treblinka guard "Ivan the Terrible." He was extradited to Israel, where he was found guilty and sentenced to death in 1988, but the conviction was overturned five years later as a case of mistaken identity.

In the latest prosecution, Demjanjuk is accused of serving as a "Wachmann" or guard, the lowest rank of the Ukrainian and other eastern European guards subordinate to German SS men. It is the first time a conviction has been sought against someone so low-ranking without proof of a specific offense.

If convicted, he faces up to 15 years in prison.