Peter Madsen initially claimed that he last saw Kim Wall when he dropped her off on the tip of an island in Copenhagen late on August 10 after she had interviewed him aboard the do-it-yourself craft.
But Madsen, who has been accused of negligent manslaughter, "told police and the court that there was an accident on board the sub that led to the death of Kim Wall, and that he subsequently buried her at sea in an undefined location of the Koge Bay" south of Copenhagen, police said in a statement.
Copenhagen police later on Monday said they found a woman's torso near Koge Bay where they carried out an intense search for Wall, a 30-year-old reporter who had been writing a feature story about Madsen, after she failed to return from an interview with him aboard the 60-foot (18-metre) Nautilus on August 10.
"When I say torso, it's a body without head, arms and legs," Copenhagen police chief Jens Moller Jensen told a news conference, adding it was "too early" to say if it belonged to Wall.
Madsen's appearance before a judge on August 12 was held behind closed doors and the investigation has been classified, so it is not known exactly when he made his statement.
But his lawyer Betina Hald Engmark told Danish broadcaster TV2 on Monday that Madsen "had always wanted" the information on the preliminary hearing to be disclosed.
'Invincible' and 'ambitious'
Wall was a freelance journalist who had reported for The Guardian and The New York Times. A graduate of the Columbia Graduate School of Journalism, she was based between New York and China.
Her friends have described her as "invincible", "ambitious" and "always seeing something good in everyone", according to Swedish media reports.
Madsen and Wall were seen onboard the vessel by several people in waters off Copenhagen the evening of August 10.
Photos of the two emerged online standing next to each other in the sub's tower. Wearing an orange fleece and with her long auburn hair tied in a topknot, she appeared to be smiling.
When Wall failed to return home, the sub was also reported missing. Rescue crews located it around a day later in Koge Bay, about 50 kilometres (30 miles) south of the Danish capital.
Just after it was found, Madsen was rescued, alone, and the submarine suddenly sank.
TV2 showed images of Madsen being questioned by police after his rescue.
When a journalist asked him what contact information he had for the missing journalist, he responded: "Only that her name is Kim."
"I don't check the background when a journalist calls and asks 'Can I interview you?'" Madsen said indifferently as he entered a police car.
'A curse lies on Nautilus'
The Nautilus was the biggest private sub ever made when Madsen built it in 2008 with help from a group of volunteers, described on a website about the vessel as "submarine enthusiasts".
The volunteers were engaged in a dispute over the Nautilus between 2014 and 2015 before members of the board decided to transfer the vessel's ownership to Madsen, according to the website.
Madsen had sent a text message to two members of the board in 2015, saying "there is a curse on Nautilus".
"That curse is me. There will never be peace on Nautilus as long as I exist," Madsen wrote in his text message, according to a post written by the volunteers in Danish on the website.
"You will never have a good feeling inside the submarine... do not throw more lifeblood into that boat."
Madsen, who was described in a 2014 book as "Denmark's Do-It-Yourself Astronaut", had wanted to launch himself into the space race before building the crowd-funded Nautilus.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)