WARNING: this interview contains spoilers!

The audience is initially encouraged to see Josef, Irene and Rolf as a vulnerable family simply trying to survive. How important was it to you that viewers form that emotional connection before the story begins to challenge their perception of who these people really are?

It was essential. The connection is not the start of the film; it is what Odessa is about.

So, not without reason, I called the meadow where we first meet the family “the Sound of Music meadow”: a father, a mother and a small boy crossing the Alps to flee an unknown danger, presumably the Nazis. Audiences have been conditioned for sixty years to root for that family. I wanted to use that conditioning, and then turn it upside down.

Historically accurate details do the rest. Josef calls his wife “Butzele,” a pet name taken from Mengele’s real letters to Irene. He has a remarkable ability to see the world through a child’s eyes. None of it is invented for the story. I also deliberately planted details that tell the viewer something is off. But by the time the tables turn, the viewer has already decided who these people are.

The film is built around the idea that trust can be earned very quickly and misplaced just as easily. How did you approach creating that sense of trust between the characters, particularly in the quieter moments where nothing overtly threatening appears to be happening?

By making the quiet moments the most meaningful. A crucial scene in the film is the one where the family stops by a mountain stream, the parents are quarrelling, and the boy is upset. Josef kneels down, takes out his penknife, and builds him a little submarine out of bark. Three pine cones inside: Mutti (mommy), Vati (daddy), and little Rolf. There is no threat to resist, so the audience lowers its guard. His kindness there is genuine. It was a skill Mengele really had. The trust between the characters is built the same way. Irene is persuaded to keep walking not by argument but by watching her husband with her son. He uses their son to convince her.

The audience goes through the same persuasion, and gives him the benefit of the doubt.

The eventual revelation changes the way we understand much of what came before. When constructing a story like this, how do you make the earlier scenes work on two levels, both as the audience initially experiences them and after they have been seen in a completely different light?

The rule I set myself was that every line had to be completely innocent on first viewing, and only reveal its deeper, gruesome meaning on the second viewing, or even after further research.

At lunch with the twin brothers, Josef is fascinated by their likeness and asks whether it has ever been useful. The first time, he is just a curious guest in a slightly strange conversation. The second time, once you know about Mengele’s fascination with twins, and that the Nazis murdered people with mental disabilities like Michael’s, it is horrifying.

When Irene watches him bandage their son’s leg and says, bitterly, “Good thing your father didn’t become a dentist,” it plays as a wife’s frustration. In hindsight, it is fate: Mengele did start out studying dentistry before switching to medicine. Medicine is what took him to Auschwitz and turned him into one of history’s most notorious war criminals.

Even his farewell carries it. He promises his son they will swim together one day, in a warm country by the sea. Mengele died while swimming in Brazil. He was never caught.

“Monsters don’t come dressed as monsters” is a striking idea at the centre of ODESSA. How did you translate that concept into the behaviour, appearances and relationships of the characters without making the film’s intentions too obvious too early?

By giving every warning sign an alibi.

There are red flags in the film from early on. Josef uses a code word to get a meal. He is unusually interested in the twins, and there seems to be a threatening tension between him and the priest. When Irene refuses to go on, a coldness surfaces in him for a moment, and then disappears. But each of these moments has an innocent explanation. A refugee would need a password. Anyone could be curious about identical twins. Two strangers in the aftermath of a war would be wary of each other. A desperate father would panic if his wife refused to go on.

That is how deception works in life. The warning signs are always there; what disarms us is that each one, on its own, can be explained away. The audience does the explaining themselves. I just made sure the explanations were available. And if you then add a redeeming trait, like being genuinely kind to children, people will mistake charm for character.

The Dolomites are such a powerful presence throughout the film. What did the landscape represent to you within the story, and how did you use the isolation, scale and harshness of the environment to reflect what the characters were experiencing?

The whole film is about duality, and the fine line between kindness and cruelty. The Dolomites are first of all historically accurate: Mengele fled over these mountains to Genoa, and onward to South America. But they were also the perfect backdrop, because the Dolomites are duality in its most natural form: astonishingly beautiful and dangerously brutal at the same time. I felt that throughout the making of the film, and the story uses all of it: the beauty, the harshness, the isolation.

The film moves through the landscape deliberately. It begins in alpine meadows, the postcard Alps, and as the journey goes on the terrain turns rawer, rockier, colder. By the time the family is running through the forest at night, the gentle mountains of the opening are gone for good. The landscape drops its mask before the protagonist does.

Isolation mattered too. The church stands alone in the fields. The brothers’ hut stands alone. The hamlet lies isolated high on a mountain. And the junction where Irene and Josef have to make their choice, one path leading up, the other down, is a desolate spot where you can see more than 80 miles into the distance.

At the end there is the Tre Cime. Josef stands looking at those three peaks, and realises that his family’s happiness is nowhere near as eternal as they are.

Choosing to shoot the film on 35mm gives the period setting a very particular texture and sense of physical reality. How did the decision to use celluloid influence the way you approached the film’s composition, lighting and overall visual atmosphere?

Celluloid has its own duality. It is a gift: the image comes out of the camera with character already in it, that warm, vintage texture I was looking for when I wrote the script. And it is merciless, especially on a six-day shoot in the Dolomites in October.

We shot 4-perf 35mm with 2x anamorphic lenses, which means each roll holds no more than four minutes of film. There was no time to improvise our way to a shot, so everything was worked out, storyboarded and rehearsed thoroughly in advance. The wide anamorphic frame also emphasized how small the family is against the mountains: fragile people in an unforgiving landscape.

Rushes took over 48 hours to come back, so we were always shooting blind. And reshoots were impossible anyway: a location we had filmed in bright sunshine, factor 50 on, was buried under 30 centimetres of snow two days later.

I wanted the film to look as naturalistic as possible, with as little artificial light as we could manage. That made every day a race against the sun. Even so, the meticulous preparation still left room for a few small, unplanned gems.

And on the last day luck finally sided with us: a complete overcast let us shoot all our blue-hour scenes day-for-night. Instead of a fifteen-minute window, we had the whole afternoon.

There is a strong contrast between the family’s physical vulnerability and the uncertainty surrounding their true circumstances. How did you work with Bastian Beyer, Magdalena Müller and Johannes Zeiler to build performances that could sustain that ambiguity while keeping the characters emotionally believable?

Bastian and Magdalena had both read a great deal about their characters, and in rehearsals we shaped them further together, particularly their ambiguous traits.

The most important note I gave Bastian was: do not play a monster. Mengele was a friend to children, and he believed he was a misunderstood man of science. The ambiguity had to come from the audience, not from him, right up until the reveal.

Magdalena plays a woman who barely knows her husband, yet chose him when she had plenty of other suitors. Because we did not shoot in chronological order, she and I kept what we called “Irene’s motivation scorecard”: for every scene, we had set a score for her state of mind during preparation, so her emotional arc stayed consistent however the schedule jumped around.

Johannes had a double challenge: he plays both twin brothers. Alois is eloquent and generous, a priest who feeds refugees. Audiences trust a priest the way they trust a father. That trust is part of the trap too, because Alois is modelled on the real network of clergy who helped Nazis escape, believing they were doing good. Michael is Alois’s vulnerable point. Johannes plays him convincingly as a mentally disabled brother who would do anything for his twin, the brother who was also his salvation during the war.

At its core, ODESSA asks audiences to question how quickly they form judgements based on appearances and how easily empathy can shape what they believe. What did you want the audience to be left questioning about the characters, and perhaps about their own instincts, once the film ends?

I would like them to ask themselves one simple question: at what moment did I decide to ignore the signs I had seen, and give him my empathy anyway? And is that something I do more often in life?

That is not a failing of the audience. It is how we are built. The instincts that have kept us safe for thousands of years tell us to trust the familiar, the gentle, the people who look and speak like us. Odessa started from exactly that question, in a conversation four or five years ago, in the wake of the Syrian refugee crisis: would we feel differently about refugees if they looked like us? And someone so good with children cannot be evil, can he?

If someone walks out of Odessa and looks a little harder at the next person who charms them, and better still, at the next person they are about to vote for, the film has fulfilled its purpose.