Martin Haas, who lost relatives in the concentration camps, says Mr Demjanjuk's behaviour was "theatre-like"
John Demjanjuk, accused of helping to murder nearly 28,000 Jews at a Nazi death camp, has gone on trial in the German city of Munich.
Mr Demjanjuk, who is 89 and was deported from the US in May, entered the courtroom in a wheelchair. His eyes were closed but he seemed conscious.
He denies being a camp guard at Sobibor, in Nazi-occupied Poland.
The trial is expected to last until May and, if found guilty, Mr Demjanjuk could be sentenced to 15 years in jail.
The trial's first session was delayed for over an hour, as large numbers of people tried to gain access.
'Hollywood, not Sobibor'
Organisers were overwhelmed by the crowds of people trying to get in, including journalists and relatives of Holocaust survivors.
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 the case should never have gone to trial, citing cases in which Germans assigned to Sobibor had been acquitted.
"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."
John Demjanjuk, a retired car worker in the US state of Ohio, stands accused of having helped the Nazi death factory to function.
Prosecutors say that, as a camp guard at Sobibor, he pushed thousands of Jewish men, women and children to their death in the gas chambers.
'Hell on earth'
Mr Demjanjuk was captured by the Nazis while fighting in the Soviet army. He denies even being at Sobibor.
DEMJANJUK CASE TIMELINE
1952: Gains entry into the US, claiming he spent most of war as German POW
1977: First charged with war crimes, accused of being "Ivan the Terrible"
1981: Stripped of US citizenship
1986: Extradited to Israel
1993: Israeli Supreme Court overturns conviction, ruling that he is not Ivan the Terrible
2002: Loses US citizenship after a judge said there was proof he worked at Nazi camps
2005: A judge rules in favour of deportation to his native Ukraine
2009: Germany issues arrest warrant; deported by US and charged
But prosecutors say statements from a now-dead Ukrainian place Mr Demjanjuk at that death camp.
The statements - which the defence says are inconsistent - say Mr Demjanjuk "participated in the mass killing of Jews".
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.
As Mr Demjanjuk is in poor health, doctors have asked that hearings should be limited to two 90-minute sessions per day.
There are no living witnesses in this case, but over 30 people listed as joint plaintiffs are expected to testify about what happened at Sobibor, described by investigators as hell on earth.
Two are camp survivors, others lost relatives or their entire families among the 250,000 people murdered there.
This is the second time John Demjanjuk has appeared in court.
Two decades ago, he was sentenced to death in Israel, convicted of being Ivan the Terrible, a notoriously sadistic guard at the Treblinka death camp.
But that ruling was overturned after new evidence showed that another Ukrainian was probably responsible.
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