A Danish court has ordered the owner of an amateur-built submarine be held in pre-trial detention for 24 days while authorities investigate the mystery disappearance of a Swedish journalist who was aboard the vessel before it sank.
The police later said Madsen had been charged with the murder of the female journalist.
The 40-ton, almost 18-meter-long (60-foot-long) vessel has been described as the largest privately built submarine of its kind.
Police have launched a search for Ms Wall, a freelance journalist based in New York and China who has written for the New York Times, the Guardian and Vice Magazine.
Before his arrest, Madsen appeared on Danish television to discuss the submarine's sinking and his rescue.
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However, when she failed to return home later that day, her anxious boyfriend contacted the authorities, which led to a full-scale search for the submarine in the early hours.
Kim Wall, 30, a NY and Beijing-based journalist, hasn't been seen since Madsen's40-ton, almost 60-foot-long submarine sank off Denmark's eastern coast Friday.
Kristian Isbak, who had responded to the Navy's call to help locate the ship on Friday, told The Associated Press he first spotted Madsen standing wearing his trademark military fatigues in the submarine's tower while it was still afloat. "They were the only two on board [on Thursday]". The inventor has denied wrongdoing and said that he dropped Wall-who was reported to be the only other person on board the submarine with him-off on an island close to Copenhagen Thursday night before the submarine sank, according to AP reports. She also was not identified by name.
The submarine is lying in 7ft of water, but divers have not been able to enter it safely yet, police said. They were hoping to tow it to port on Saturday and open it then, the statement said. "I design and manufacture non-commercial extreme machines, employing teams of volunteering engineers and technicians to challenge the ordinary". "Diving, no matter the method, is very challenging and it*s technically hard to go to beyond where rubber suits and scuba gear can take us".
According to a timeline compiled by police, on Thursday at about 7 p.m. local time (1700 UTC), the sub departed Refshale Island, a former industrial shipyard transformed into a creative hub, for what was supposed to be a short trip. Two helicopters and three ships combed the sea from Copenhagen to the Baltic Sea island of Bornholm. Madsen was the owner of the sunk submarine.