Mr Demjanjuk says he was a prisoner of war of the Nazis during World War II
John Demjanjuk, a Ukrainian-born retired car worker from the US city of Cleveland, Ohio, is being tried in Germany for the murder of more than 27,000 Jews at a Nazi death camp.
In 1986, Mr Demjanjuk was deported by the US to Israel, accused of being "Ivan the Terrible", the notorious prison guard at the Treblinka extermination camp.
The Israeli Supreme Court later overturned his conviction and death sentence for war crimes, when evidence emerged suggesting he was not the same guard.
He then returned to the United States, but seven years ago an immigration judge ruled that there was enough evidence to prove he had been a guard at several Nazi concentration camps.
Mr Demjanjuk was stripped of his citizenship, but remained in the US while the authorities decided what to do with him.
Then in March, German prosecutors said they had charged him with more than 29,000 counts of accessory to murder in connection with his alleged time as a guard at the Sobibor death camp in Nazi-occupied Poland.
He became number one on the list of the world's most-wanted suspected Nazi war criminals.
US federal agents briefly removed him from his home in April, but a stay of deportation was granted after his family said he was too ill.
The following month, the Court of Appeals in Ohio ruled that the deportation could go ahead, saying it was satisfied that Mr Demjanjuk would be provided with adequate care in Germany. On 11 May, he was flown from Cleveland to Munich and taken into German custody.
His trial is expected to be Germany's last big war crimes trial.
The 89-year-old was born Ivan Demjanjuk in 1920 in the Ukrainian village of Dubovi Makharintsi.
The US says Mr Demjanjuk's wartime ID proves he was a death camp guard
Mr Demjanjuk joined the Red Army after the outbreak of World War II, and fought until he was captured by German troops in eastern Crimea in 1942.
He testified during his trial in Israel that he was held as a prisoner of war at a camp in Chelmno until 1944. He was then transferred to another in Austria, where he joined an anti-Soviet Russian military unit funded by the German government with whom he fought until the end of the Allied victory, he said.
In 1952, Mr Demjanjuk emigrated to the US, eventually settling in Cleveland, where he worked as an engine mechanic at a car plant.
But 29 years later, he was temporarily stripped of his US citizenship after a judge ruled that he had lied in his citizenship application about his wartime activities.
DEMJANJUK CASE TIMELINE
1951: Gains entry into the US, claiming he spent most of the war as a German prisoner
1977: First charged with war crimes, accused of being "Ivan the Terrible"
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
2006: Loses appeal against deportation
2008: Loses final Supreme Court appeal
2009: Charged on 29,000 counts of accessory to murder in Germany; deported by US
According to a 2002 US district court ruling, reliable evidence suggests that Mr Demjanjuk was in fact an "an armed guard at Sobibor, where 250,000 men, women, and children were murdered; at the Majdanek concentration camp, where at least 170,000 civilians died; at the Flossenbuerg concentration camp, where some 30,000 civilians perished; and a member of a unit trained at the Trawniki Training Camp to implement 'Operation Reinhard', the Nazi programme to dispossess, exploit, and murder Jews in Poland".
The Trawniki unit, named after a village in eastern Poland, was made up of Ukrainian volunteers from Red Army soldiers held prisoner by German forces. Its members were trained by the Nazis to help run camps in Central and Eastern Europe.
One member of the unit, known as Ivan the Terrible, was a Wachmann (guard) for the Waffen SS at the Treblinka death camp. There, he helped operate the gas chambers and personally murdered hundreds of prisoners, hacking many of his naked victims to death with a sword, according to witnesses.
In 1983, Israel issued an extradition request to the US, accusing Mr Demjanjuk of war crimes. Prosecutors said he was the notorious Ivan the Terrible.
During his trial, Mr Demjanjuk's lawyers argued that he was the victim of mistaken identity and challenged the accuracy of the memories of five Treblinka survivors who identified him as Ivan the Terrible.
Israel's chief justice was careful to avoid declaring Mr Demjanjuk innocent
However, an ID card showing that he had been registered at the Trawniki training camp helped sway the judges in the prosecution's favour. In 1988, he was found guilty and sentenced to death by hanging.
His conviction was eventually quashed in 1993 by the Israeli Supreme Court, after evidence hidden in the archives of Russia's former KGB intelligence service until the previous year suggested that another Ukrainian man, named Ivan Marchenko, had been the true Ivan the Terrible.
The Israeli chief justice was, however, careful to avoid declaring Mr Demjanjuk "innocent", saying there was ample evidence that he had served as a guard in concentration camps other than Treblinka.
After walking free, Mr Demjanjuk returned to the United States, where, in 1998, his citizenship was restored after a judge found that the US Justice Department had acted with "reckless disregard for their duty" in 1981.
For the first time we have even found lists of names of the people who Demjanjuk personally led into the gas chambers
German prosecutor Kurt Schrimm
But in 2002, his citizenship was once again revoked. A district court judge ruled that even if Mr Demjanjuk was not Ivan the Terrible, there was still sufficient reliable evidence to prove that he had been a concentration camp guard.
Mr Demjanjuk appealed in 2004, but judges upheld the decision. A year later, a court ruled that he should be deported to his native Ukraine, Germany or Poland.
In 2008, the Supreme Court rejected his final appeal. He remained in the US, however, while officials tried to decide where he should go.
Then in November 2008, state prosecutors in Munich, where Mr Demjanjuk lived briefly after the war, said they had enough evidence to prove his involvement in the murders of tens of thousands of Jews at Sobibor between March and September 1943.
US government surveillance video showed Mr Demjanjuk walking without help in April
They said they had managed "to obtain hundreds of documents and also found a number of witnesses who spoke out against Demjanjuk".
"For the first time we have even found lists of names of the people who Demjanjuk personally led into the gas chambers," said Kurt Schrimm, head of the special office investigating Nazi crimes.
Mr Demjanjuk's lawyers initially won him a temporary stay of deportation after charges were filed in March, saying he could not travel to Germany because of ill-health, but an immigration appeals board and the US Court of Appeal both later rejected the argument.
In April, the Simon Wiesenthal Centre made him number one on its most-wanted list of Nazi war criminals. Efraim Zuroff, director of the centre in Jerusalem, said the move reflected the importance of efforts to deport Mr Demjanjuk to Germany so he could stand trial.
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