Auschwitz is made even more horrifying by the simple fact that someone had to dream up its atrocities in the first place. One of those people was Rudolf Höss, an SS officer who was tasked with devising a method to efficiently kill Jews. As commandant of the notorious concentration camp, Höss oversaw the use of Zyklon-B pesticide, sometimes donning a gas mask himself to supervise the mass murder of what he estimated to be 2.5 million victims. After World War II, Höss was sentenced to death at the Nuremberg Trials, and hanged in 1947.

But Höss’s son Hans-Jurgen Höss, now 87, never knew the commandant as a monster. Even though his family lived a few hundred yards from the concentration camp, separated from it by just a garden and a high concrete wall, Hans grew up oblivious to his father’s awful truth. Hans and his young siblings were told that the camp, inside occupied Poland, was a prison and their father ran it. The family was privileged: They had a pool and staff—and some of Hans’s happiest memories were from that early-1940s period in Auschwitz. (The Höss family’s dissonantly idyllic home life was recently dramatized in the Oscar-winning narrative film The Zone of Interest.)

When filmmaker Daniela Volker first contacted Hans several years ago, he was in such denial about his father’s role in history that he hadn’t even read the memoir Höss had written in prison. “It was too painful and just too much to deal with,” Volker says. “I understood pretty much the first time I met him that Hans-Jurgen Höss had spent 80-something years avoiding dealing with who he was. He had an extremely idealized vision of his father, because at home, the father he knew was a loving, kind, wonderful father—actually, for the 1940s, very involved with his children, whenever work permitted it. Auschwitz seemed to be the place where he’d been happiest as a child, unaware of what was happening beyond the garden wall.”

Hans’s idea of his father was at complete odds with the man who wrote matter-of-factly in his memoir about enabling mass murders. “It was almost like a true-crime story in which the criminal wrote his deathbed confession,” says Volker, who was “absolutely floored” to discover the autobiography existed.

Volker says that it took her about a year to convince Hans, through his pastor son Kai, to face his father’s legacy—and to do so on camera in The Commandant’s Shadow, a documentary in theaters May 30. Asked why she thinks Hans finally felt ready to confront the past, Volker suggests it was part age, part logistics. “I came along and sort of facilitated it,” she explains. While filming, Hans returned to his childhood home and visited the concentration camp his father oversaw for the first time. “We organized the trip, so it didn’t require any more effort beyond turning up,” Volker says. “I don’t think psychologically he would’ve been able to actually organize it.”

In The Commandant’s Shadow, Hans’s confrontation with his father’s past climaxes when he meets Anita Lasker-Wallfisch, a 98-year-old survivor of the Auschwitz hell that Höss commanded. “I persuaded [Hans] that it’s important, not just for him but for the historical record, to document the encounter of two eyewitnesses who saw Auschwitz from two really, very different sides,” says Volker. “He had to overcome himself in order to be able to do it. But he understood why it was important.”

Lasker-Wallfisch’s life was spared only because she played cello. Her lawyer father and violinist mother were killed upon arrival at Izbica, a transit ghetto in Poland. But the Auschwitz guards apparently took their entertainment seriously, and needed a cellist for the orchestra they had assembled from the prisoner population. Lasker-Wallfisch and the other “lucky” musicians played marches morning and night amid the camp’s horrors.

“Their circumstances couldn’t have been more different,” says Volker of her film subjects. “He lived in utter luxury. She was in a barrack. She was lucky she was a musician because they had better food—not that that was much to talk about, but at least they had better rations.”

Lasker-Wallfisch, who has spoken publicly about her experiences during the Holocaust, didn’t flinch at the idea of welcoming Hans into her London sitting room. In the scene, Hans is understandably nervous when he greets the Auschwitz survivor. It is Lasker-Wallfisch, a no-nonsense type with a cigarette in hand, who puts Hans at ease.

“It was brave of you to do this,” she tells him, piercing the tension in the room. When Hans tells her, referring to his father’s actions, “We live with the guilt,” Lasker-Wallfisch replies, “You weren’t asked whose son you want to be.” She later concludes, “You can’t forgive what happened but the important thing is that we talk to each other and understand each other.”

Volker didn’t know what would happen when the two came face-to-face. “It was interesting—they were both, of course, German, so they spoke German to each other. You realize that these people were quite similar. They came from close families. [Lasker-Wallfisch’s] father was a World War I veteran, so was [Hans’s]. And they were separated by ideology. It makes you think about the power of ideology. In another life, maybe Höss would’ve been a car salesman and would’ve sold the most cars of anyone in Germany. But he just happened to subscribe to this deadly, crazy ideology.”

Hans and Lasker-Wallfisch were joined in the meeting, and in the documentary, by their adult children—Hans’s son Kai and Lasker-Wallfisch’s daughter Maya, a psychoanalyst, both of whom have been indelibly shaped by their parents’ histories. In The Commandant’s Shadow, they describe haunted childhoods in which their parents refused to discuss their pasts, and the way that second-generation secrecy and trauma impacted them.

“Whether a descendant of a victim or a perpetrator, in a way what happens is quite similar—it’s the silence which is corrosive and toxic, and the sensation of knowing that something very wrong is there, lingering,” says Volker. The filmmaker wanted to capture “the shock waves that events in the past sent down the generations. The past is not just the past—it’s important because it ripples down. It has an effect on the present, and we can learn from it.”

The generational effect of trauma is something that Lasker-Wallfisch’s daughter Maya has spent her life untangling. After surviving a lonely childhood and drug addiction, Maya became a psychoanalyst. She wrote a memoir about her family, Letter to Breslau, that was published in German. Mother and daughter had a relationship that was, at times, difficult; given what Lasker-Wallfisch had experienced at Auschwitz, she could not wrap her mind around Maya’s suffering. At one point, Lasker-Wallfisch told Maya that she was not the right mother for Maya—a line that devastated Maya, and that Lasker-Wallfisch repeats in the documentary. “I was emotional,” Maya explains. “I had human needs, as every human does.”

Now, Maya says in an interview, she and Lasker-Wallfisch have reached a point of understanding in their relationship: “She gets it now completely. She gets how her absence was devastating for me.”

The making of the documentary brought mother and daughter slightly closer too. Lasker-Wallfisch appreciated that her daughter went to Auschwitz to accompany the commandant’s son on his first trip to the concentration camp, giving him a tour of the hellscape his father supervised.

“His terror was greater than mine, and his suffering was greater than mine in terms of what he had to grapple with,” recalls Maya, who found herself, as a psychoanalyst, wearing many hats throughout that emotionally grueling day with Hans. “I was being my mother’s daughter, Maya the therapist. All the time I’m conscious of the whole dynamic that is unfolding, so it was hard. But it should be hard.”

When Maya visited her mother afterward, Lasker-Wallfisch greeted her in an uncharacteristically warm manner. “Her words to me were, ‘Welcome home, hero. Tell me everything,’” Maya recalls, savoring the memory. “The film relieved me of one thing: I got to make my mother proud.”

The sit-down between Hans, the Auschwitz commandant’s son, and her mother, the Auschwitz survivor, happened about a day after this triumphant homecoming. Inside Lasker-Wallfisch’s home, both she and Hans marveled at the fact that they were coming together amicably given their pasts.

“A historic moment,” Lasker-Wallfisch said.

“Who would have thought it?” Hans replied.

The survivor is not one to waste breath on adjectives, but afterward she called the meeting with Hans “beautiful.”

“That’s not a word that she commonly uses for anything, including her own daughter,” Maya points out. “But for the word to come out of her mouth in that context.… She was just so remarkable in her generosity.”