Géza Röhrig's visit to Auschwitz in the 1980s changed his life. "I lost faith in man, and that created a void," said Mr Röhrig, now 48. Into that void came God.

Now he has returned to the camp - albeit to a set recreated in army buildings near Budapest, Hungary - as the lead actor in Son of Saul, a feature film that has won the Grand Prix at Cannes, a Golden Globe for Best Foreign Language Film, and is nominated for an Oscar.

The second "visit" was transformative for the Hungarian-born actor, who now lives in New York City with his wife and children. "There was no 'same man' any more. I am a different man," he said.

Through the fictional character of Saul Ausländer (Röhrig), Hungarian writer and director László Nemes' film - part-funded by the Conference on Material Claims Against Germany - ushers us into the hell of the Sonderkommando, a zone within Auschwitz where specially selected prisoners were forced to see Jews to their death in the gas chamber, and then prepare for the next arrivals.

Members of the Sonderkommando were themselves gassed, usually after a few months, and replaced by new prisoners. The same basic procedure was followed at the other camps, including Belzec, Chełmno, Majdanek, Sobibór and Treblinka. Very few survived.

Mr Röhrig said he and Mr Nemes "shared a strong frustration with the genre" of Holocaust movies, "those stupid Hollywood monologues portraying people as if in a normative reality.

"This was not about making a horror movie," said Mr Röhrig. Sound plays a major role. "The viewer doesn't have to see things with his eyeballs… but it's harder because he's going to see it with his soul."

To get ready for the role, Mr Röhrig took a leave from teaching Judaic studies at Solomon Schechter high school in New York.

"It was a lonely preparation," he said. "I wanted to know what a day was like in the Sonderkommando. The hair cutting, the disinfection, the gas chamber, the burning, the minutiae."

Mr Röhrig also internalised Mr Nemes' mission "to clarify some of the misconceptions about the camps, especially about the Sonderkommando.

"Most people entertain themselves with the issue of complicity [in the genocide] and I find the whole topic obscene," Mr Röhrig said. "Every attempt to shift the burden of guilt towards the victims has to be rejected." And yet the way other prisoners viewed the Sonderkommando is not ignored.

"We hated those people," admitted Auschwitz survivor Marian Turski, addressing some 700 people at a special Berlin screening of Son of Saul. "We hated them more than we hated the Germans" because "they were from my people… and because they were also - like myself - inmates, and they lent a hand in the killing process."

Later, Mr Turski understood that he could easily have ended up in the Sonderkommando. "I am absolutely sure that their suffering was much greater… than my suffering."

For Mr Röhrig at age 17, the death camp was the scene of an awakening. "I walked out of Ozwiecem" - the Polish town that the Germans renamed Auschwitz - "fully committed to go all the way." He became observant. "That's not to say I'm taking God off the hook. But God's responsibility does not cancel the autonomy of humans. Yes, God survived the Holocaust. And I really mean by the skin of his teeth."