The right-wing British historian David Irving pleaded guilty to criminal charges of denying the Holocaust and conceded he erred in contending there were no Nazi gas chambers at Auschwitz as his trial opened today in Vienna.
Irving, 67, told reporters he now acknowledged that the Nazis systematically slaughtered Jews during the Second World War.
"History is like a constantly changing tree," he said as an eight-member jury and a panel of three judges prepared to hear charges that could put him behind bars for up to 10 years.
Irving, handcuffed and wearing a navy blue suit, arrived at the court carrying a copy of one of his most controversial books - "Hitler's War," which challenges the extent of the Holocaust.
He has been in custody since his arrest in November on charges stemming from two speeches he gave in Austria in 1989 in which he was accused of denying the Nazis' extermination of six million Jews.
A verdict could come later today.
Irving's trial comes amid new - and fierce - debate over freedom of expression in Europe, where the printing and reprinting of unflattering cartoons of the Prophet Muhammad has triggered violent protests worldwide.
Irving had tried to win his provisional release on 20,000 euros (£13700) bail, but a Vienna court refused, saying it considered him a flight risk.
His lawyer, Elmar Kresbach, said last month the controversial Third Reich historian was getting up to 300 pieces of fan mail a week from supporters around the world, and that while in detention he was writing his memoirs under the working title Irving's War.
Irving was arrested on November 11 in the southern Austrian province of Styria on a warrant issued in 1989. He was charged under a federal law that makes it a crime to publicly diminish, deny or justify the Holocaust.
Within two weeks of his arrest, Irving asserted through his lawyer that he had come to acknowledge the existence of Nazi-era gas chambers.
In the past, however, he has claimed that Adolf Hitler knew little if anything about the Holocaust, and has been quoted as saying there was "not one shred of evidence" the Nazis carried out their "Final Solution" to exterminate the Jewish population on such a massive scale.
Vienna's national court, where the trial is being held, ordered the balcony gallery closed to prevent projectiles from being thrown down at the bench, the newspaper Die Presse reported yesterday.
It quoted officials as saying they were bracing for Irving's supporters to give him the Nazi salute or shout out pro-Hitler slogans during the trial, which will continue into tomorrow if a verdict is not reached today.
Irving is the author of nearly 30 books, and has contended most of those who died at concentration camps such as Auschwitz succumbed to diseases such as typhus rather than execution.
In 2000, Irving sued American Holocaust scholar Deborah Lipstadt for libel in a British court, but lost. The presiding judge in that case, Charles Gray, wrote that Irving was "an active Holocaust denier ... anti-Semitic and racist".
Irving has had numerous run-ins with the law over the years.
In 1992, a judge in Germany fined him the equivalent of £3,500 for publicly insisting the Nazi gas chambers at Auschwitz were a hoax.Reuse content