As Mirka survived in hiding, the man who would become Mora's father, Georges (a German Jew born as Gunther Morawski), fought alongside Philippe's future godfather, the legendary mime artist Marcel Marceau, in the French Resistance. "It turns out that a lot of my family were what you'd call 'fighting Jews'," says the director, proudly. "There's an antisemitic myth that the Jews went quietly into the gas chambers. It's nonsense. There was a lot of fighting and a lot of protest."
Eight of his father's family did die in Auschwitz, however. And when Mora attended a 2010 retrospective of his films in Wroclaw, Poland, where his paternal grandparents had been married, he was able to learn more about them in archived documents that the Nazis hadn't had time to destroy before the Russians swept through.
"I couldn't believe the names of all my family members. I knew they'd died, but here it was in black and white.
"One name that struck me was Charlotte Morawski, who did a thesis on Nietzsche, in 1915, in Breslau [the German name for Wroclaw] University. There was a notation in her file that said: 'Charlotte Morawski has asked for the photo of her father to be given to the local synagogue when she is evacuated.' Evacuated was the term the Nazis used for Auschwitz/murder."
To his horror, he discovered that the Nazis had gone through the house of a "comparatively very wealthy" great uncle, and valued every item "down to each cup, each plate, each chair. . . The value of taps. The value of toilets. It wasn't just murder. It was a huge looting, a robbery, and then kill the victims and no one will know."
As Auschwitz wasn't far from Wroclaw, Mora decided to go to the camp to pay tribute to his dead relatives. Three Days in Auschwitz emerged from this and subsequent visits, over a period of five years, as the film-maker - whose documentary Swastika shocked the Cannes film festival in 1973 by attempting to make sense of Hitler through intimate home movies shot by Eva Braun - struggled to find an "explanation for humans doing this to other humans".
He began with a plan but, as each door he opened led to numerous other doors, the project became increasingly personal, until he reluctantly found himself in front of the camera, effectively scratching his head and wondering how you even make a film on the subject. "Every time I tried to analyse it, I came up to that wall of, 'What happened? How do you do this,'" he says. "So I just thought: 'I'm going to drive myself crazy here. Just do it and see where the cards fall.' In one way, it's more like a painting than a movie."
In the film, he actually tries to convey some of the violence of the Final Solution through paintings he did inspired by Munch's The Scream (a foreshadowing of the Holocaust, he suggests) and Francis Bacon's post-Shoah work, though he questions the power of art to influence and change people.
Anti-Hitler artists in Germany "were on to it, the horror, before it all happened," he says. "But the sad thing is, it didn't stop the war." A few years ago, in Madrid, the sight of a group of schoolchildren studying Picasso's Guernica moved him. "[But] what is the effect of art," he asks. "What is the effect of a movie? It's certainly overpowered by bombs, to put it crudely."
In a quote at the beginning of the documentary, Goebbels tells Germans to "hang on" and one day they will be the subject of a colour film that will be elevating, rather than one that makes people "hoot and whistle". Three Days in Auschwitz is Mora's slightly bewildered response to the twisted ideology that resulted in the murder of six million (possibly more) Jews, and the delusion of the Nazi regime.
The camp itself is now "the largest cemetery in the world", says Mora, who, when he visited Auschwitz for a fourth time last year, was told that the number of visitors is "increasing exponentially".
This is heartening at a time when antisemitism is surging and social media is being used to spread Holocaust denial. Mora recalls a quote he read from a professor: "'Denial is a second genocide.' That struck me because, if you deny this happened, you are creating a false reality. A counterfeit reality. Which is very, very dangerous."
He views attempts by people on the internet to whitewash the Holocaust as particularly disturbing. "At first, I ignored it, but I think it's dangerous to ignore it. I think you just have to calmly fight with facts. The true fanatics, you can't convince them. The nuts are the nuts. It's the people who think, 'Oh maybe that's true,' they're the ones that have to be nipped in the bud."
Maybe Three Days in Auschwitz, which is intimate, unconventional, highly personal, and furnished with a haunting Eric Clapton score that could help it to reach a different kind of audience, can play a small role in this.
Art alone may not be able to hold back the darkness, but that doesn't mean it isn't worth doing - especially when 24 hours are all that have separated your existence from oblivion.
