'Into the Deep: The Submarine Murder Case' - who is Peter Madsen? The disturbing story behind the Netflix film

Netflix's true crime documentary Into the Deep: The Submarine Murder Case follows the disturbing story of Peter Madsen - but who was he and what did he do?

Unusually, the documentary began filming nearly a year before he committed murder, but continued throughout Kim Wall's disappearance unfolding and Madsen's court case.

Find out more about the inventor, his horrific crimes and the strange tale of his actions afterwards.

How can I watch Into the Deep: The Submarine Murder Case?

The documentary is a film that is currently streaming on Netflix.

It has been available since 30 September.

Who is Peter Madsen?

Peter Madsen is a Danish inventor who is convicted of killing Swedish journalist Kim Wall.

He became famous for building a home-made, crowd-funded submarine and was attempting to become the world's first amateur astronaut by constructing his own space rocket when he was contacted by Australian filmmaker Emma Sullivan.

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She began filming a documentary about his life and work, which included working alongside a number of science and engineering students who saw him as an inspirational figure, but 11 months into filming Wall, who had interviewed him on his submarine, disappeared and Madsen was implicated.

Into the Deep features a number of disturbing interviews with Madsen in which he jokes about violence and murder, discusses whether he is a psychopath, and voices his frustrations with others, all of which played a part in his murder conviction.

What happened to Kim Wall?

Journalist Kim Wall had been due to move to Beijing, but missed her own leaving party when she was given the opportunity to interview Madsen aboard his submarine and spend the night on it in August 2017.

A chilling picture used in the documentary shows Wall and Madsen on board the submarine before it went underwater, and in her final text to her boyfriend, Wall wrote: "I'm still alive btw. But going down now. I love you!"

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Sullivan was filming the day after the interview and captured on film the reactions of Madsen's Copenhagen lab staff as they heard reports that the man they had thought to be their friend and mentor had gone missing along with the submarine.

He was quickly found to be alive and well, but the submarine was disastrously damaged and he claimed to have dropped Wall off on shore before the problems started.

But with Wall's boyfriend confirming she had never returned, the lab staff's reactions turned from disbelief to horror as they learned that Madsen had been accused of her murder.

Parts of Wall's dismembered body were discovered sunk in the water nearby and Madsen originally claimed to have disposed of her after a submarine hatch accidentally hit her on the head, killing her.

When her head was discovered with no injuries, he changed his story to accidental poisoning, but he was convicted of murder in part because of testimony from his staff and footage from Sullivan that showed it had been premeditated - in one scene, a saw that he used can be seen in the background but is missing on the day he is preparing to meet Wall.

Madsen was found to have large amounts of disturbing porn and torture footage on his computer and appeared to have planned to murder the next woman to board the submarine, with Wall being the unlucky person to have joined him.

Is Peter Madsen in jail?

Into the Deep shows Sullivan and former members of Madsen's lab staff outside court as his life imprisonment sentence is read out in April 2018.

He is currently in prison in Denmark but in October 2020, managed to escape and was found in a nearby residential area.

Madsen appeared to have a pistol and a belt full of explosives, but they turned out to be decoys and he was taken back to prison.

In 2020, Madsen married a Russian activist who has political asylum in Finland, but they divorced in January 2022.

What does identity digitally disguised mean?

One of Madsen's former staff and friends, "Sara", is labelled during the documentary as having her identity digitally disguised in her interview scenes.

Sara talks about her trauma at realising someone she was close to committed such horrific crimes and gave key evidence against Madsen at his trial.

During her scenes, she shows messages arranging to spend time on the submarine with Madsen the night after Wall's murder, sent before Wall's visit happened, and says she believes it is possible Madsen had been planning to kill her before another woman joined him on the boat first.

A work-in-progress version of Into The Deep premiered at Sundance film festival in 2020, but afterwards two participants were removed from the film and “Sara” asked to be digitally disguised.

The filmmakers used cutting edge technology which provides a lifelike disguise but offers a more authentic viewing experience to the audience than a blur.

Watch: Submarine killer recaptured after prison escape