Martin Haas, who lost relatives in the concentration camps, says Mr Demjanjuk's behaviour was "theatre-like"
A lawyer for John Demjanjuk, accused of helping to murder 27,900 Jews at a Nazi death camp, has accused German prosecutors of double standards.
Mr Demjanjuk, 89, denies he was a guard at Sobibor camp, in wartime Poland.
As the case began in Munich, his legal team said in previous cases Germans assigned to the camp had been cleared.
The Ukraine-born accused, who was extradited to Germany from the US in May, was twice carried into court, first in a wheelchair then a stretcher.
Doctors have said Mr Demjanjuk is in poor health, and asked that hearings be limited to two 90-minute sessions a day.
Over 60 years after the end of World War II, this may be Germany's last big war crimes trial.
But the BBC's Oana Lungescu in Munich says that, as the first to focus on a low-ranking foreigner rather than a senior Nazi commander, it breaks new legal ground.
AT THE SCENE
Oana Lungescu, BBC, Munich
After a delay of 70 minutes John Demjanjuk entered the court in a wheelchair, wearing glasses and a dark blue baseball cap, and covered in a blanket. He mumbled at first , but then settled down to listen to a Ukrainian interpreter - his eyes apparently shut.
His lawyer immediately went on the offensive - accusing German judges of double standards. "How can John Demjanjuk, a Ukrainian prisoner of war, be found guilty," he asked, "when several German SS officers, who served in the death camps, have been previously acquitted."
Facing Thomas Blatt, an 82-year-old survivor of Sobibor, the defence lawyer said he and John Demjanjuk were both victims.
Defence lawyer Ulrich Busch said it should never have gone to trial.
"How can you say that those who gave the orders were innocent... and the one who received the orders is guilty?" Mr Busch told the court.
"There is a moral and legal double standard being applied today."
Mr Busch has said even if it could be proved his client - who was captured by the Nazis while fighting in the Soviet army - was in Sobibor, he would have been there under duress.
A retired Ohio car-worker, Mr Demjanjuk stands accused of having helped the Nazi death factory to function.
Prosecutors say he was a guard who pushed thousands of Jews to their deaths in the gas chambers at Sobibor.
Lawyers for Mr Demjanjuk - who denies being at the death camp - say he will not speak at all during the case.
The trial is expected to last until May and, if found guilty, Mr Demjanjuk could be sentenced to 15 years in jail.
If Mr Demjanjuk is acquitted it is not clear where he will go as he has been stripped of his US citizenship.
A leading French Nazi-hunter voiced disappointment over the case as he said the accused would only have been a minor figure.
Serge Klarsfeld told AFP news agency on Monday: "It's a bit disappointing - a bedridden non-German, occupying a subordinate position and who would have died of hunger in a prison camp" if he had refused to serve as a guard.
'Hollywood, not Sobibor'
Mr Demjanjuk arrived on Monday in an ambulance at the courtroom, which was crowded with people, including journalists and relatives of Holocaust survivors.
DEMJANJUK - PROSECUTION CHALLENGES
89 years old, health failing
Described by prosecution as low-ranking guard
No death camp survivors to testify against him personally
Prosecutors relying heavily on about 30 joint plaintiffs and circumstantial evidence
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