In April 2018, he was convicted of the August 2017 murder of Swedish journalist Kim Wall on board his submarine, UC3 Nautilus, and sentenced to life imprisonment.

While attending primary and secondary school in Høng, Madsen developed an interest in rocket fuel with the help of chemistry and physics teacher Johannes Fischer.

[9][10] Madsen continued to experiment and to consult engineers, and became friendly with the family responsible for the fireworks in Copenhagen's Tivoli Gardens.

He also joined the Dansk Amatør Raket Klub (DARK) rocket club in Copenhagen,[11] but the other members gradually became disillusioned with him.

[24] On 11 August 2017, Madsen was arrested after the sinking of UC3 Nautilus and the disappearance of Kim Wall, a Swedish journalist who had last been seen alive aboard the submarine.

[29] According to the Danish police, the submarine was deliberately sunk, contradicting Madsen's explanation regarding a technical fault.

[28] A human torso washed up on the coast of Amager on 21 August, which DNA tests concluded belonged to Wall.

[30] Chief investigator Jens Møller reported that the torso had been stabbed multiple times to vent accumulating gases that could float it to the surface, and that a piece of metal had been fastened to it to ensure its sinking to the seabed.

[32] During a hearing on 5 September, Madsen stated that Wall had been killed when he lost his grip on the submarine's hatch cover, which he was holding open for her, and it hit her on the head, causing her skull to fracture.

[34] A post-mortem examination of the torso found "knife wounds to her genitals and ribcage", believed to have been caused "around or shortly after her death".

[35] On 30 October 2017, it was reported that Madsen had changed his account of Wall's death and admitted dismembering her body.

It was later confirmed by the police that he had made no clear statement on how she had died, but had said that she was inside the submarine when it contained exhaust gases.

When police discovered that he was in possession of a pistol-like object and was wearing a belt that could potentially contain explosives, he was surrounded until bomb experts had determined that it was a decoy.

[50] On 9 February 2021, a Copenhagen court handed down a 21-month prison sentence to Madsen, for his attempted escape from jail.

It features Søren Malling as chief inspector Jens Møller, Pilou Asbæk as special prosecutor Jakob Buch-Jepsen and Rolf Lassgård and Pernilla August as Wall's parents.

The TV series does not feature the crime itself and does not mention Madsen's name, whose character does not appear onscreen either; it focuses on the investigative work leading to his indictment and conviction.