Ed Mosberg reaches into his wardrobe, and takes out his concentration camp uniform. He buttons it neatly, and forces the striped hat onto his now elderly head. His teenage years were spent in the Krakow ghetto, then the nearby Plaszow concentration camp under the capricious, sadistic rule of the commandant made notorious by Schindler’s List, Amon Göth, then as a slave labourer in the Mauthausen-Gusen camp in Austria, and finally the Hermann Goering factory in Linz.

On 5 May 1945, with their Nazi captors on the point of defeat, he and his fellow slaves were ordered into dynamited caves. They lived because the dynamite failed. Mosberg’s family of 16, including his parents and sisters, had already been murdered.

When he was filmed putting the uniform back on in 2015, he was back at Mauthausen for the 70th anniversary of the camps’ liberation, where he walked through gasping tourists, a living, stubborn rebuke to industrial murder. This forms the opening scene of a new Holocaust documentary, Destination Unknown, which offers new testimonies, but also asks how the camps’ victims have survived the rest of their lives.

Mosberg is 92 now, as he sits across from me in London, smartly dressed in blazer and tie. Back in New Jersey, where he and his wife, fellow camp survivor Cesia, have made their home, he is a successful, sometimes controversial property developer, and he makes calls on his iPhone before our interview, still very much in the world around him. But his former, nightmare world is also literally close enough to touch.

Outside Block 11 (Death Block) in Auschwitz concentration camp

“It was my [camp] uniform [in the film], yes,” he confirms. “With my number on it.” Then he leans close to show me a metal plate like a large dog tag, which he is wearing on a metal chain, with the number 85454. “This is the original number. With two holes, and you wear with wires on your wrist.” I realise later that this plate must have been on Mosberg in Plaszow. Putting the uniform on, too, must surely be painful. “I just put it on so that people know that something did exist. I don’t do this for pleasure. It hurts me. Okay? But I have to do it. Because for as long as I live, I will do it.”

Mosberg shows little interest in the indulgence of analysing how the Holocaust changed him. Instead he’s here to implacably bear witness, as he has in countless forums before. But his forcefulness in Destination Unknown as, still in his striped uniform, he barges his wheelchair-bound wife through the Mauthausen crowds, does suggest a man who no longer bothers with backward steps.

“That’s his character,” the film’s British director, Claire Ferguson, tells me. “When he wants something, he will go for it. When he has his wife in a wheelchair, he will do everything to get her where he needs her.”

Llion Roberts, the British producer who instigated the film and spent a decade assembling its testimonies, agrees. “Ed would always be ahead of you, and you’ve got to catch up. He still does 100 press-ups every morning, at 92, and 10 minutes on the treadmill in his apartment. He wants to get from A to B, and he wants to go now. They all move out of the way in the film, because he’s going so fast.”

Mosberg was 13 when the Nazis invaded Poland in 1939. I ask him how life had been for a Jewish boy in Krakow before then. “I never saw any anti-Semitism before the war,” he states.

When, then, did he realise the extent of what the Germans were doing to Jews? “When they start making ghettos,” he says flatly, in his still strong Polish-Jewish accent.

“In 1941,” he remembers, “they declare that all the Jews from the city of Krakow have to move to another location. And we had a big apartment, my grandparents had a big apartment. One of my aunt’s had an apartment, she was a lawyer, another one was also. They moved us all together to one apartment with two bedrooms. So many people. And then they started making the ghettoes smaller. So they started moving people out. My grandparents, my parents’ cousins. They told me that they had to go resettle in another part of Poland. They brought them into Belzec. Belzec was not a concentration camp. Belzec was an extermination camp. And they were murdered there.”

Mosberg carrying the Torah at the 2017 March of the Living between Auschwitz and Birkenau

The idea of a survivor type seems redundant in such terribly circumscribed conditions. Still, I ask Mosberg if he resolved to survive, in part to protect his family. He is composed till now. But this brings two long, bottomless sighs.

“There was no way to protect,” he says. “No way to protect. I did once. And then I made a mistake.” He sounds angry, and desperately upset. He’s thinking of the way he kept his sisters in the back line when the Nazis selected who they’d kill, till the day they reversed the lines’ order, condemning his sisters. “I never want to talk about it,” Mosberg says. “But Mr. Roberts made me talk. I never talk about it because it bothered me all my life.”

They lived longer because of you, I tell him. Ed Mosberg looks back at me, unpersuadable.

He was perhaps 15 when he was trying to save his family. Did what he saw make him think less of humanity? “Well those people were not human beings,” he answers. “They were murderers. They did this for satisfaction. Amon Göth, I worked in his office, so I saw what he was doing. He did this for pleasure. To take dogs, and let the dogs rip up the people. He stood and was shooting people from the balconies. When he was walking through the camp, you knew that somebody would get killed.”

Mosberg was reunited with Göth when he was put on trial then hanged by the Allies. “I saw him in jail,” Mosberg recalls. “And you want to know something? He was guarded by two policemen at that time. And I was still afraid of him. I was afraid. I don’t know why. I lived in Krakow after the war, but I never went to Plaszow. I was afraid to go. And I’m not a person where I’m afraid of anything. I don’t know why.” But he does. “Because Plaszow reminded me of my mother. I give her a piece of meat, and she spit it out and she said, ‘This is not kosher’, she cannot swallow it, and the next day they took her to her death [in Auschwitz in 1944]. And the same thing, when my two sisters were taken there. So, I was afraid to go.”

A typical style of train used for transports to the camps which is preserved at the Yad Vashem museum

Mosberg and his wife Cesia moved to the US in 1951, where there was initially little interest in what they’d suffered. “When I said to some people the story about the Holocaust, they said, ‘Don’t think, sir, we had it so easy here. We couldn’t buy a steak,’” he recalls with bitter irony. “I was laughing.”

But he did return to the camps, with his young, American family. “It’s close to 50 years already,” he considers. “Because I remember I was carrying my daughter Caroline in my arms up the steps of Mauthausen, and my wife was worried. I said, ‘I could carry at that time boulders. I can carry my child.’” Roberts filmed Mosberg in 2004, hoisting a boulder on his 79-year-old shoulder as he climbs the camp’s 186 steps, as he once did daily, on pain of death. Did managing that make him stronger inside?

“Yes. It made me stronger,” he says. “Because if someone was walking up the steps and he dropped the boulder, it went down and broke the legs of the other prisoners. And the top of that wall, they called the parachute wall. They lined up the Jews there and told them, ‘You have to push the one in front of you.’ Ok? And they didn’t have no choice. And they were just falling down being killed there. I don’t know if this made me stronger. It made me not to forget it. Stronger? If you see people being killed, it don’t make you stronger. And I saw killing all the time. When they liquidated the ghetto. How they were beating people, shooting them, I was there,” he says fiercely, looking me straight I the eye. “I saw it.”

Destination Unknown’s makers believe their film is timely, in the face of resurgent racism and anti-Semitism, and an “apathy” Roberts sees growing towards the Holocaust, as its witnesses die.

Mosberg, though, doesn’t see what he experienced as repeatable, whether in Rwanda, or the future. He sees the Nazis as uniquely vicious robbers, from Kristallnacht till the end. “Even Amon Göth, at the end, was arrested for taking belongings for himself. Pope Benedict when I met him, went into the Bundestag and said, ‘We Germans know the best that the Nazis were gangs of robbers.’”

Mosberg is wholly forgiving of Germany today, knowing that “99 per cent of Germans from before then are not alive any more. If there is still some anti-Semitism there, I don’t have to go into Germany or Poland. I find it in the United States. People don’t like it when I say it, but this is the truth.”

Mosberg, a staunch Republican, doesn’t, though, lay blame for this with President Trump’s populism. “It doesn’t worry me,” he says of the world’s fractious state. “Because it never happens as the same thing it was before. This is politics. Now because of this President, they’re saying there’s [more] anti-Semitism. There was always anti-Semitism.”

Another survivor in Destination Unknown, Marsha Kreuzman, says she dreams of walking on snow, which is the bones of her fellow victims. Does Mosberg have a recurring nightmare?

“Well, I have many times dreams about the Holocaust, yes. But my wife, she has it constantly. Two days ago, she was calling for her mother. She was calling for her sisters. She said, ‘I want to put me into the water. I want to drown like they were drowned.’ I say, ‘Don’t say that.’ And this is the way I live, with my wife,” he says heavily. “We’ve been married for 70 years.” Ed Mosberg, like many of the survivors, was left alone in the world by the camps. His love with Cesia has clearly helped that hollowness.

“Two days ago I wasn’t sure I was coming here, because I didn’t want to leave my wife,” he continues. “But I asked her. I said, ‘I’m going to London. She said, ‘For what?’ I said, ‘The movie, and I have to talk, that our family will be remembered. And also the other people in other families and the rest of the people who were murdered. She said, ‘Okay, go.’” The Holocaust may seem like it could fade into history. But not while Ed Mosberg remembers.