A new drama tells the story of a Jewish lawyer who confronted Hitler 80 years ago - earning the dictator's life-long hatred. So who was Hans Litten?
In the Berlin courtroom, Adolf Hitler's face burned a deep, furious red.
The future dictator was not accustomed to this kind of scrutiny.
But here he was, being interrogated about the violence of his paramilitary thugs by a young man who represented everything he despised - a radical, principled, fiercely intelligent Jewish lawyer called Hans Litten.
The Nazi leader was floundering in the witness stand. And when Litten asked why his party published an incitement to overthrow the state, Hitler lost his composure altogether.
"That is a statement that can be proved by nothing!" he shouted.
Litten's demolition of Hitler's argument that the Nazis were a peaceful, democratic movement earned the lawyer years of brutal persecution.
He was among the first of the fuehrer's political opponents to be rounded up after the Nazis assumed power. And even long afterwards, Hitler could not bear to hear his one-time tormentor's name spoken.
But although he was among the first to confront Hitler, Litten remains a little-known figure.
Now a drama and an accompanying documentary tell the story of a cantankerous, flawed but ultimately heroic man.
Litten was, long before he confronted the dictator, a staunch anti-Nazi. Although his father, a law professor, had converted from Judaism to Christianity and played down his background to further his career, the young Litten went in the opposite direction, joining a Jewish youth group and learning Hebrew out of a mixture of adolescent rebellion and sympathy for the dispossessed.
As a lawyer, he specialised in defending workers and rank-and-file members of the German Communist Party (KPD). However, he was no Stalinist, clashing with the KPD leadership for following Moscow's orders. "Two people are too many for my party," he would say.
Indeed, his hard-line adherence to his principles meant Litten was not always regarded as sympathetic character.
"He was a saint. But I have a feeling that, if I sat down to have a beer with him, I wouldn't like him," says Benjamin Carter Hett, author of Crossing Hitler: The Man Who Put the Nazis on the Witness Stand, a biography of Litten.
"He was in many ways a difficult man to deal with. He was doctrinaire in his politics. Even his closest friends said he wasn't good with people."
However, it was Litten's belligerence, as well as his forensic intelligence, that made his interrogation of Hitler so effective.
In 1931, Litten sought to have criminal charges brought against four members of the Nazi party's Sturmabteilung (SA) paramilitary group after they attacked a dance hall frequented by communists, killing three people.
Litten called Hitler as a witness, hoping to expose the Nazi party's deliberate strategy of overthrowing democracy by bringing terror to the streets. Hitler had previously assured middle-class voters that the SA was an organisation dedicated to "intellectual enlightenment".
Over three hours in May 1931, this claim was dismantled by Litten's precise, detailed questioning.
At first, Hitler insisted to Litten that he was committed to "100% legality". But his composure began to crack when Litten asked him why he had been accompanied by armed men. "That is complete lunacy," the Nazi leader barked.
But the decisive blow came when Hitler was asked why the Nazi party had published a pamphlet by Joseph Goebbels, Hitler's chief propagandist, which promised the movement would "make revolution" and "chase parliament to the devil" using "German fists".
Asked by Litten how Goebbels's rise up the Nazi hierarchy could be squared with a commitment to legality, Hitler began to stammer and "search convulsively for an answer", according to one contemporary newspaper report of the trial.
According to World War II historian Laurence Rees, writer and director of the television series Nazis: A Warning from History, it was not Litten's focus on the Nazis' violent methods that enraged Hitler the most. By 1931, most Germans could not fail to have noticed that the SA were brutal streetfighters, he says. And Hitler himself was accustomed to - and indeed thrived on - the venomous abuse directed at him from opponents.
But, he says, Litten's meticulous, carefully reasoned questioning was guaranteed to enrage him.
"What drove Hitler berserk is that here is someone taking him coolly and calmly through the evidence," says Rees.
"He hates that kind of intellectual argument - he prefers either haranguing or sulking. It's not just Litten's Jewishness. If you were going to come up with a person that Hitler would loathe, it would be him."
The trial was widely publicised and marked out Litten as a hate figure in the Nazi press, which called for him to be physically attacked.
As Hitler edged closer to power, friends urged Litten to flee Germany. But he refused. "The millions of workers can't get out," he said. "So I must stay here as well."
Soon the Nazis were in control. When the new regime used the Reichstag fire in February 1933 as an excuse to suspend civil liberties, Litten was among the first to be rounded up.
Over the next five years he was held in a succession of notorious concentration camps including Sonnenburg, Dachau and Buchenwald. He was singled out for especially brutal treatment at the hands of the guards, who knew full well of the fuehrer's personal antipathy towards him.
Nonetheless, throughout his incarceration he was admired by his fellow inmates for his kindness towards them and his insistence on keeping his dignity intact. When the guards ordered prisoners to stage a performance in celebration of a Nazi anniversary, Litten read out a poem called Thoughts Are Free.
By February 1938, he could endure no more. He took his own life by hanging himself. He was 34.
After the Nazi regime was finally smashed, Litten's reputation as a staunch opponent of Hitler was revived. A plaque in Berlin was dedicated to him in 1951, the headquarters of the German bar association is at Hans Litten House and the lawyers' association of Berlin named itself itself the Hans Litten Bar Association after reunification.
Yet his name is not widely known. According to Mark Hayhurst, who wrote and directed the BBC drama and documentary about Litten, he was a victim of cold war politics - his left-wing sympathies meant he was overlooked in the West, and his attacks on the Stalinist hierarchy caused him to be neglected in the Soviet Bloc.
With these divisions now buried for a generation, Hayhurst hopes that Litten can be reclaimed as a figurehead for resisting tyranny.
"There are still Hans Littens around the world today," he says. "He's still an inspiration."