Underwater horror: Shocking details about the murder of journalist Kim Wall, killed in Danish inventors homemade submarine

Peter Madsen, a self-taught Danish engineer and inventor, had a favorite pickup line he liked to use on women: “You want to see my submarine?”It wasn’t a joke.In 2008, when Madsen was 37 , he constructed the UC3 Nautilus, which at the time was the largest amateur submarine in the world.

He built it in his private lab, in a shipyard lab off the coast of Copenhagen, Denmark.Though he was married at the time, he would often “frequent BDSM clubs and private fetish parties,” seeking out what he called “a web of ‘crazy ladies’ on the side,” writes Matthew Gavin Frank in his new book, “Submersed: Wonder, Obsession, and Murder in the World of Amateur Submarines” (Pantheon), out June 3rd.His obsession with submarines (and women) ended with deadly consequences.

On August 11, 2017, he agreed to take Swedish journalist Kim Wall, who was writing a story about him, on a brief submarine journey in Køge Bay.The 30-year-old woman was brutally assaulted and murdered by Madsen, who was 46 at the time.Wall’s torso washed up on a beach almost two weeks later, and her various other body parts were eventually discovered.

Madsen was accused of torturing Wall before killing her, dismembering her body, and having “sexual relations other than intercourse of a particularly dangerous nature,” according to court records, with stab wounds found in and around Wall’s genitals.It was shocking that Madsen, who had no previous history of violence, could commit such a horrifying crime.But as Frank argues, a passion for submarines “can ruin a person for the surface,” and sometimes the compulsion to sink to great depths can “dovetail with darker, more threatening traits.”Madsen may have acted alone, but he was part of an “eccentric micro-community of DIY submersible enthusiasts,” writes Frank.

And their fascination with underwater travel might be symptomatic of something more sinister than just Jacques Cousteau fantasies.Since 2002, the PSUBS (or “personal...