Into the Deep Netflix: The True Story Behind the Submarine Documentary That Almost Didn't Happen

When Emma Sullivan started filming Peter Madsen in 2017, she thought she was making a quirky portrait of a self-taught Danish engineer. A dreamer. A guy building his own space program and submarines in a dusty Copenhagen workshop. It was supposed to be a feel-good story about DIY science and the power of human ambition. But then, on August 10, 2017, Swedish journalist Kim Wall stepped onto Madsen’s submarine, the UC3 Nautilus. She never came back.

Watching Into the Deep Netflix is a disorienting experience. It isn’t your typical true crime documentary where a crew shows up months later to interview neighbors and police officers. Sullivan was already there. Her cameras were rolling before, during, and after the murder. It’s raw. It captures the exact moment the "dreamer" persona slipped and revealed something much darker.

The Footage That Became Evidence

Most people don't realize how close this film came to never existing. After the murder of Kim Wall, the volunteers and interns working for Madsen were broken. They had been part of his "Lab," a community built on the idea of doing the impossible. Suddenly, their mentor was a suspected killer. Sullivan sat on a mountain of footage that suddenly looked like a psychological roadmap to a crime.

The documentary captures the immediate aftermath with a chilling intimacy. You see the volunteers' faces as the news breaks. First, confusion. Then, the desperate hope that it was just an accident—a mechanical failure. Finally, the sickening realization that they had been helping a monster. This isn't just about a murder; it's about the betrayal of a community.

Why the Into the Deep Netflix Version We See is Different

If you followed the production of this film, you might know it faced significant hurdles. Several people featured in the original cut, which premiered at Sundance in 2020, eventually asked to be removed. They didn't want their trauma or their association with Madsen to be a permanent digital footprint.

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Netflix and Sullivan had to pivot.

They used digital masking—basically a high-tech blur or "deepfake" style overlay—to protect the identities of those who no longer wanted to be part of the narrative. This adds a surreal, almost ghostly layer to the film. You see the movements and hear the voices, but the faces are altered. It serves as a constant reminder that these are real people whose lives were genuinely wrecked by Madsen's actions.

The Psychology of Peter Madsen

Madsen was a master of "performative genius." He knew how to talk to the press. He knew how to inspire young, idealistic engineers. But Sullivan's footage catches the cracks. There’s a specific scene where Madsen talks about his "darkness." At the time, it probably sounded like edgy, tortured-artist talk. In hindsight, it’s a confession.

He wasn't just building rockets. He was building a cult of personality.

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The Timeline of a Tragedy

The events of August 2017 moved fast, but the documentary slows them down to a painful crawl.

• August 10: Kim Wall boards the UC3 Nautilus for an interview.
• August 11: The submarine is reported missing. Madsen is rescued from the sinking vessel; Wall is nowhere to be found.
• August 21: A torso is found washed ashore.
• October 2017: Madsen’s hard drive is found to contain snuff films and videos of women being tortured.

The most damning part of Into the Deep Netflix isn't the physical evidence, though. It's the psychological shift. We see Madsen's texts. We see his mood swings. The film effectively dismantles the "eccentric inventor" trope. It shows that sometimes, "eccentric" is just a mask for "predatory."

A Documentary About the Bystanders

What makes this film stick in your throat is the perspective of the volunteers. They weren't just background characters. They were his friends. They were his hands and feet in the workshop. The documentary forces us to ask: If we were there, would we have seen the signs?

Or would we have been blinded by the "coolness" of building a submarine?

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The film doesn't give easy answers. It shows the volunteers grappling with immense guilt. They gave him the tools. They gave him the space. They gave him the social cover he needed to operate. It’s a brutal look at how predators use the passions of others to hide their own depravity.

What Most People Get Wrong About the Case

There’s a common misconception that this was a crime of passion or a sudden break from reality. The footage suggests otherwise. Madsen was calculating. He had been planning something for a long time. The "accident" he initially claimed—that a hatch fell on Kim Wall’s head—was debunked by the sheer amount of forensic evidence and Sullivan's own footage of his behavior leading up to the trip.

He invited other women onto the sub in the days prior. Kim Wall just happened to be the one who said yes on that specific night. It’s a terrifying thought. It was a crime of opportunity meeting a long-gestating fantasy.

Technical Precision in the Investigation

The Danish police work featured in the story is incredible. They didn't just find the sub; they rebuilt the timeline second by second. They used ocean current modeling to find the remains. They used digital forensics to peel back the layers of Madsen’s private life. But Sullivan’s film provides the "why" that the forensics couldn't quite capture. It provides the vibe. The atmosphere of the workshop was one of intense pressure and "genius-worship," which is exactly the kind of environment where a person like Madsen thrives.

Actionable Steps for True Crime Viewers

If you’ve watched the film or are planning to, there are a few things you should do to get the full context of the case. The documentary is a masterpiece of editing, but it’s only one piece of the puzzle.

1. Read Kim Wall’s work. She wasn't just a "victim." She was a brilliant, courageous journalist who wrote for The Guardian, The New York Times, and Vice. She was in Copenhagen to tell a story about the intersection of gender and science. Check out the Kim Wall Memorial Fund to see how her legacy continues to support female journalists.
2. Look into the Danish "Deepfake" Controversy. Research how the film used "anonymization technology." It’s a fascinating look at the future of documentary ethics. How do you tell a true story when the witnesses want to be erased?
3. Compare the versions. If you can find the 2020 Sundance reviews, compare them to the Netflix release. Seeing how the narrative shifted once certain people dropped out is a lesson in the power of film editing.
4. Check the legal outcomes. Peter Madsen was sentenced to life in prison. In 2020, he briefly escaped but was caught within hours. Knowing he is behind bars makes the viewing experience slightly less haunting, but only slightly.

The story of the UC3 Nautilus isn't a mystery anymore. We know what happened. But Into the Deep Netflix remains essential viewing because it shows us the face of a killer before he knew he was being watched. It's a warning about the danger of putting "geniuses" on pedestals and the heavy price of ignoring the red flags hiding in plain sight.