The man accused of Kim Wall’s torture, murder, and dismemberment always dreamed that his D.I.Y. mini submarine, the UC3 Nautilus, would attract global attention. Today, the vessel, covered in a green tarpaulin, in the unlovely industrial landscape of Nordhavn, at the edge of Copenhagen, has indeed achieved international fame—not as a feat of engineering but as a crime scene. In the course of Peter Madsen’s circuitous, self-mythologizing, and often bizarre testimony at his trial for the murder of the Swedish journalist, it has become clear that, to the man who built it, the Nautilus was always far more than a submarine. For a decade, the boat functioned variously as a publicity platform, a sex venue, a crash pad, an underwater hideout, a potential round-the-world record breaker and—according to the prosecution—a film set. But for Madsen, above all, the Nautilus was a work of art.

Madsen’s vessel was the world’s largest privately built submarine; its launch, in Copenhagen Harbor, in May of 2008, was a festive event, with local and international media showing up to watch Madsen’s associates in the art collective Half Machine perform a “ballet” on the deck of the watercraft. The Danish news magazine Ingeniøren quoted Madsen as claiming that the Nautilus represented “a political message about individual freedom,” and the port’s blog quoted the man, then known as “Peter Submarine,” as declaring: “I build things to tell stories.” Madsen often said that the 1981 German film “Das Boot” provided him with the aesthetic inspiration for the Nautilus, and that its name came from the submarine in Jules Verne’s “Twenty Thousand Leagues Under the Sea.” From the beginning, Madsen’s stories were derivative rather than original.

The year of the Nautilus launch, 2008, was a busy one for Madsen, who was embedded in the Danish art fringe and living full time inside the cramped Nautilus. A week after its launch, he joined with the rocket-builder and architect Kristian von Bengtson to form a collective of amateur rocket-makers, Copenhagen Suborbitals, with the dual mission of launching Madsen into space in a crowdfunded, open-sourced rocket and opening up space travel to the public. But Madsen’s and von Bengtson’s lofty creative collaboration—and their friendship—fell apart, in February of 2014, when Madsen accused his collaborator of prioritizing his family over their rocket-building. Tired of Madsen’s accusations, von Bengtson quit the project. But he wasn’t the only member of the group uncomfortable with Madsen’s style. By the summer of that year, the remaining Suborbitals—who saw Madsen as argumentative and uncoöperative—effectively ejected the man now going by the moniker “Rocket Madsen.” Insulted and angry, Madsen responded by setting up his own outfit, Rocket Madsen’s Space Lab, and declaring “war” on his former associates.

It was in the long, embittered wake of this fallout, in March of 2017, that Kim Wall, who was pitching a story to magazines about the Danish “space race,” made her first contact with Madsen. During the decade that Madsen had spent promoting his engineering projects, Wall had been acquiring a prestigious education at the Sorbonne, the London School of Economics, and Columbia University, and establishing herself as an international journalist. Drawn to outsiders and what she called “undercurrents of rebellion,” Wall reported from all over the world for publications such as the Times, The Atlantic, and the Guardian. She wrote about feminism in China, the oppressed Pardhi tribe in India, nuclear waste in the Marshall Islands, and, most recently, in Harper’s, the underground Internet culture in Cuba, where “during the height of the Cold War, Beatles records (illegal, imperialist propaganda) were smuggled inside the cover sleeves of regime-approved rumba bands, and American radio blasted from transistors hidden in flower pots.”

At the time that Wall chose to write about the Madsen-Suborbital clash, not only was she living in Copenhagen but she and Madsen were neighbors: she had recently moved in with her Danish boyfriend in the funky Refshaleøen district, once a thriving industrial area around Denmark’s largest shipyard, Burmeister & Wain, and now home to several creative shared office spaces—including Rocket Madsen’s Space Lab.

Since the opening of the trial, on March 8th, the testimony has revealed that Wall was just one of a string of young women the amateur engineer had invited on a ride in the Nautilus in the spring and summer of 2017. Several of these women were among the thirty-six witnesses who have appeared in Copenhagen City Court so far. (Madsen’s wife, who initially supported him but divorced him earlier this year, was excused from giving evidence on health grounds.) During ten days of court proceedings spread across four weeks, the judges heard sober, bizarre, shocking, and mind-boggling testimony from rocket enthusiasts, submarine experts, a forensic pathologist, and members of Copenhagen’s sexual underground—including a witness from The Black Society, a B.D.S.M. group that kicked Madsen out for being “too passive.” Together, their testimonies assembled a portrait of a personality without boundaries: a fantasist, a genius inventor, a tech nerd determined to break world records for space and submarine travel, and a man sexually obsessed with snuff movies featuring the torture and murder of women.

On the afternoon of August 10th, Madsen texted Kim Wall, responding to an interview request that she had made back in March. Surprised but pleased that her “space race” story might develop after all, she paid him a visit at his Space Lab, where they had a cup of tea. She left, planning to go on a submarine trip with him later that evening. Then, according to the prosecution, Peter Madsen stashed a saw, sharpened screwdrivers, straps, pipes, and a video camera in the hold of the Nautilus, and sometime after 7 P.M. welcomed Wall onboard. She waved goodbye to her boyfriend and friends, who had gathered to celebrate the couple’s forthcoming move to China, and the submarine slipped beneath the calm surface of the Baltic.

What Madsen may or may not have told Wall over their cup of tea, but which may turn out to have significance, was that his other pet project had recently received a blow. He had intended the launch of his new rocket—characteristically christened Alpha—to mark his “victory” over the Suborbitals. But sudden cash-flow problems prompted Madsen—to the surprise of the project’s collaborators—to abort the take-off, which had been scheduled for August 26th. In the wake of his decision, Madsen appeared dispirited to some witnesses; to others, manic. On the day of the Nautilus’s final voyage, one trial witness saw him walking purposefully through a crowd of festival-goers with a saw sticking out of his backpack. The Australian director Emma Sullivan, who interviewed Madsen for a documentary earlier in the afternoon of Wall’s visit—and who had filmed with him in the submarine a few days earlier—described Madsen as having a “a strange energy.” During the interview, Madsen suggested that he might be “psychopathic”—a diagnosis that would later be backed up by a psychiatric evaluation that added “narcissistic tendencies” and a “severely aberrant” sexuality (but not insanity) to the mix. According to the evidence, Madsen had run an Internet search for the terms “beheading,” “girl,” and “agony” the night before the atrocity—a search that lead him to a video of a throat-slitting. It was, allegedly, far from the first murder-as-entertainment that Madsen had watched. The police found searches for the beheadings, hangings, and fatal impalement of women on his hard drives, along with an archive of torture, snuff, and execution videos. With his Alpha project thwarted, could Madsen have seized on a new “project”: a snuff movie starring Kim Wall, with the submarine as a film set, and himself as auteur? We may never know the answer, but this seems to be the case the prosecution is methodically building against him.

Before Madsen took the stand, he sat subdued next to his defense lawyer, Betina Hald Engmark; he was clad in dark leisurewear, with dishevelled hair and eyes half-hidden by glasses. He appeared at times bored, and at times intently engaged, as the prosecutor, Jakob Buch-Jepsen, laid out the central evidence for the charges against him. But when Madsen’s turn came to testify he seemed excited and energized, clearly aware of the hundred or so journalists from all over the world following the proceedings in the courthouse. Madsen, appearing by turns naïve and nonchalant, admitted to having lied earlier to investigators, but stuck to his third, most recent version of events: that Kim Wall had suffocated after inhaling fumes from a malfunctioning engine while Madsen was locked out on the deck. Madsen’s lies were a form of “protection,” he explained—not for himself, but for Wall’s parents. He wanted to spare them the “gruesome tale” of what actually happened.

It was at this point that his testimony became more surreal. Several times, Judge Anette Burkø interrupted his repetitive and chaotic account of technical minutiae to insist that he “stick to the essentials.” Continuing his version of the evening’s events, Madsen referred to himself in both the first and the third person, frequently switching between present and past tense: “Kim was having the time of her life” and “Peter is talking a lot, he is happily sharing his dreams with Kim,” and using “she” to refer to both Wall and the Nautilus. When he spoke of her “lying there quietly without a sound” it was unclear whether he was referring to Wall’s corpse on the floor of the submarine, or the Nautilus stranded on the sea-bed. Later, in a gruesome evocation of the art collective Half Machine’s declared “human-machine fusion” aesthetic, he conflated them again: kneeling beside the lifeless Wall, he “smacked her cheeks to try and reboot her.”

“Terminator 2” was one of the many movies Madsen referred to in his testimony, and during his court appearance it was hard not to speculate that the creations of “Peter Submarine” and “Rocket Madsen”—be they the midget sub in which he could explore the deep sea, or the tiny womb-like rocket capsule that would catapult him into space—reflected their maker’s conscious or unconscious desire to become, like the “Terminator,” a cyborg or a “half machine.”

During the next hearing, Madsen’s shaky grasp of the difference between life and art emerged again: explaining how he dismembered Wall’s body, he apologized for his account “sounding like a bad movie,” and when confronted with the suggestion that the snuff videos on his computer had inspired him to mutilate the journalist’s body, Madsen claimed that, on the contrary, watching women suffer brought out his “empathy” and was cathartic. He argued that, in this way, snuff movies were no different from Hollywood blockbusters like Quentin Tarantino’s “Kill Bill” or David Fincher’s “Se7en.” He seemed clearly unable or unwilling to acknowledge the difference between real beheadings of women and their fictional representations.

The Danes use the word grænseoverskridende to describe the inappropriate or perverse transgression of boundaries. If Madsen used his inventions to “tell stories,” they were stories that featured him as the lone, pioneering hero who smashes terrestrial frontiers and enters extreme realms, far from humankind—at the expense of other people. According to the case that the prosecution is developing against Madsen, his final “story” bears tragic witness to a ruthless commitment to the “personal freedom” he claimed the Nautilus represented. We might never find out what happened the night his submarine became the place where Kim Wall and all the future stories of an extrovert, a life-curious journalist, died. But other stories will flourish in the wake of her loss. Wall’s family and friends have set up a fund in her name, The Kim Wall Memorial Fund, to support young women in journalism. “This will be a way for everyone to focus on the future instead of it all ending that night on the submarine,” her mother, Ingrid Wall, said before the trial. “Her legacy will live on.” Meanwhile, the prosecution has demanded a life sentence for Madsen and the destruction of the Nautilus after the trial, marking the end of what Madsen called his “art.”