Even growing up in Denmark, director Janus Metz Pedersen heard about the infamous “Unabomber” case, the nickname given to the American terrorist, Ted Kaczynski, who murdered three people and injured 23 more by sending them homemade bombs through the mail.

“It was still on the news when I was a teenager, in Denmark,” Metz told Decider in recent Zoom interview. But what the director didn’t know—and what he’s willing to bet most viewers who watch his new Netflix movie, Unabomber, also don’t know—was that as a young man, Kaczynski was a participant in an unethical psychological study that exposed him to extreme stress.

“He a guinea pig in these experiments in mind control and brainwash at Harvard at very young age,” Metz explained. The Unabomber movie, starring Jacob Tremblay as Kaczynski and Russell Crowe as professor Henry Murray, endeavors to tell this story via two timelines. The first is set in the early 60s, during a young Kaczynski’s time at Harvard. The other is set in the ’90s, during the final days of the Kaczynski manhunt and eventual capture by the FBI. Shailene Woodley stars as a fictional FBI Agent named Joanne Miller, likely based on real FBI agent Molly Flynn, who received linguistic evidence gathered by a private investigation team.

But the FBI would have never caught Kaczynski without his brother David, the one who hired the private investigation and tipped off the bureau. David Kaczynski has spoken and written about his brother many times over the years, including in the recent Netflix docuseries, Unabomber: In His Own Words. Though David has a small role in the film, played by actor Matthew Kevin Anderson, Metz told Decider the production did not speak to him about the film.

“We never spoke to David, as such,” Metz said. The director spoke to Decider about why that was, as well as why a key part of Kaczynski’s real arrest was left out the film.

How much did you know about the Unabomber case before the film? What were you surprised to learn?

It’s a very American story, and I grew up in Denmark. But even though I’m Danish, it was still on the news when I was a teenager, in Denmark. So I remember it from that time. But what really drew me to the script was the fascination of these Harvard experiences, and how that story was told as a cross-cut narrative between the the manhunt in the 90s, where we find Ted Kaczynski. People know how the story ends. You’re building up to that end point by cutting back to the past, and adding, I think, something that isn’t known to most people—that he [Kaczynski] a guinea pig in these experiments in mind control and brainwash at Harvard at very young age.

Tell me about the research process. Did you watch any particular documentaries or read any particular books?

Sam Chelson and Nelson Greaves—who crafted the script and worked on the story for many years before I even got involved—did a very deep dive as part of their script work. When I got involved you know, obviously, I read as much and saw as much as I possibly could. I read the manifesto, everything. As a director you need to do to educate yourself and to push the story forwards. I looked at every possible thing I could find on Ted Kaczynski.

Ted’s brother David, who’s obviously a huge part of why the Unabomber was caught, has spoken a lot about his brother publicly and written some books. I’m wondering, did you guys speak to him at all about this? Does he know about the film?

David has been so outspoken about the story that I think it’s pretty clear what David has to say. We’re looking at all of that. We never spoke to David, as such, in person. But I think all of [his] reflections on you his relationship to his brother, their childhood, what it meant for him to give him in. It’s on the record, and we were obviously taking all that into account, as part of the process.

Jacob Tremblay and Russell Crowe have this wonderful tension that bubbles over in this final debate scene between them. Can you talk about kind of casting and working with them.

The heart of the story, to me, is the relationship between a young Ted and Professor Murray, Russell Crowe’s character. It’s a father-son story, in many ways. Ted starts to see Henry Murray as a surrogate father, in a way. He’s seduced into that relationship, only to find out that things aren’t as he thought they were.

I always start seeing certain actors in certain roles pretty quickly. Russell Crowe was one of the first people that came into my mind for the Murray character. He’s got so much gravitas as a personality, as an actor. He’s the right age. He can be very charming and very seductive, but he can also have this demonic dark side. It’s the Jekyll and Hyde personality, which was was everything that we needed from the Murray character. And somehow he feels organic to that whole Harvard, Ivy League, maybe because we know him from A Beautiful Mind. Fortunately, he responded very quickly to the material and was interested.

Jacob Tremblay, I knew him as a child actor from Room, and he was brought to my attention. I was fortunate to see some material from films that have come out that hadn’t come out at the time, that really excited me. I had a meeting with Jacob, and he was so mature in his understanding and perception of acting, and of the Ted Kaczynski character. Obviously he’d read the script. I intuitively felt this guy’s perfect, because he’s so fresh and curious. We needed to start off Ted in that, when we when we first meet him in our story. I could see that Jacob was someone who had the chops to really look for the authenticity of the emotional evolution of this character. I never looked back after that first meeting. I never considered anyone else for it.

Can you tell me about building the tension in that final, climactic sequence in post? We’ve got the debate between Ted and his professor, and then the manhunt where we’re finally capturing the Unabomber. I was struck by how you built tension without gunfire, explosions, or chase scenes.

Yeah, it’s a great thriller without any shots being fired, really—spoiler alert, on that one! It is a two-timeline story, right? You have the Harvard years, which is late 50s, early 60s, and you’re cross-cutting with the capturing of the Unabomber, in the mid-90s. These two timelines have to come to a conclusion together. It was all about trying to get that moment to be as intense as possible—finding the right cutting structure between the two timelines, because that’s something that wasn’t written that way. For some reason, all of my movies have double timelines. I don’t know if I’m particularly attracted to that. But it’s given me a solid experience of how do you get those two timelines to register into each other—[how to] build tension off of each other. Cross-cutting is the key and to do that in the most efficient and exciting way. That was really how we tried to build and capture the ending of the film.

Reading about David Kaczynski, and I saw that he turned his brother into the FBI on the condition that the death penalty not be pursued, a promise that the FBI went back on, leading to David to become an anti-death penalty activist. Why was that part of the story not included in the film?

There was so many interesting details and nuances about the story, that we had to walk a very tight line in trying to make the film that we wanted to make. As much as the story between David and Ted is an endlessly fascinating and tragic story, and heartbreaking story, it wasn’t the main focus of our film. This is a film that’s about the agent that caught Ted, and about the relationship between Ted Kaczynski and Henry Murray. When you craft a film like that, then those are the choices you make to make the story that you are telling transpire in the most effective way. Sometimes that comes at a cost of all the very, very interesting elements that did happen in real life around the Ted Kaczynski story.