PETER MADSEN: DID A DANISH ENTREPRENEUR SINK HIS HOMEMADE SUBMARINE WITH A JOURNALIST ABOARD?

The Danish inventor charged with manslaughter over the suspected death of a Swedish journalist wanted to fly into space and once said he was "a curse" on the submarine at the centre of the case.

Peter Madsen, 46, was rescued after his DIY submarine, the UC3 Nautilus, sank off Copenhagen at about midnight last Thursday.

Swedish journalist Kim Wall, 30, was on the submarine just before it sank and has not been seen since. Madsen said he dropped her off before the sinking, but he's facing a manslaughter charge as investigators search for her body.

The story is a big deal in both affected countries: It has been the lead story, or featured prominently, on news websites including Denmark's main English-language newspaper the Copenhagen Post, and Sweden's largest newspaper, Helsingborgs Dagblad — not to mention the international coverage.

WHO IS PETER MADSEN?

Peter Madsen is a self-taught aerospace engineer who calls himself an "inventrepaneur". He "designs and manufactures non-commercial extreme machines, employing teams of volunteering engineers and technicians to challenge the ordinary".

From 2001-2008 he built three submarines — the seven-metre-long UC1 Freya , launched in 2002 and decommissioned in 2006, the 12.6-metre-long UC2 Kraka , launched in 2005 and now an exhibit at Denmark's Technical Museum in Helsingor, and the UC3 Nautilus.

He has moved on from submarines to spaceflight, but has kept a firm grip on the Nautilus through multiple changes of ownership and acrimonious business breakups.

HE REALLY HAS HIS OWN SUB?

Yes, the Nautilus was designed by Madsen and built by 25 members of a submarine society named Ubadsklubben Freya after the first boat.

It is 17.76 metres long, displaces about 40 tonnes and although it can carry up to eight people, it can be operated by just one person from the captain's chair.

In contrast, Australia's Collins class submarines are 77.42 metres long, displacing 3,407 tonnes and crewed by a normal complement of 58.

At the 2008 launch in Copenhagen Harbour, the Nautilus was billed as the " longest and tallest privately-built submarine in the world".

Local newspaper Berlingske, which attended the launch, said Madsen looked "like a boy just before the birthday gift was unpacked".

He told Berlingske he would sleep in the submarine the first night and wanted to move into it, and said he had built it "because you can".

An FAQ on the Nautilus website says it is legal in Denmark to "build submarines and boats for private personal use up to 23.9 metres without any permission or control" — although a navigation exam is needed to captain a vessel of the Nautilus' size.

Nautilus was operated successfully for many years and in 2009 helped game developers from Ubisoft find inspiration for the submarine computer game Silent Hunter 5, which was released in March 2010.

In January 2011, Nautilus was taken on shore for upgrades and an overhaul expected to last several months but was not launched again until April 2017, after a fund-raising campaign on Indiegogo and an acrimonious period of ownership.

WHAT HAPPENED OVER OWNERSHIP?

In 2014 Mr Madsen founded the UC3 Nautilus submarine association to manage ownership, however in 2015 his relationship with the board of the association broke down.

In March 2015, a post on the submarine association's website said they had been in ownership conflicts over the last two months and: "The lack of confidence in long-term cooperation with Peter Madsen has unfortunately been confirmed."

"Peter Madsen's announcements have changed course — sometimes up to several times daily," the post said.

On Sunday 29 February 2015, Mr Madsen released a statement saying: "I have no plans or wishes to have any relationships with the submarine Nautilus in the future."

However, on the Monday evening, two members of the association's board said they received a text from Mr Madsen saying: "You may think that a curse is lying on Nautilus.

"That curse is me. There will not be peace of Nautilus for as long as I exist. You can not lift that curse legally."

The text continued, exhorting the board members to "not throw more blood into that boat".

The association decided to transfer ownership to Mr Madsen.

WHO IS KIM WALL?

She is a Swedish freelance journalist who studied in Paris, London and New York and has lived in New York and Beijing.

Ms Wall has been published in the New York Times, South China Morning Post, TIME and the Guardian among others.

She was writing about Mr Madsen and his submarine at the time of her disappearance, according to Swedish and Danish reports.

WHAT HAPPENED ON THURSDAY NIGHT?

Ms Wall joined Mr Madsen for a voyage leaving Copenhagen some time on Thursday.

Towards midnight, Mr Madsen was rescued from the sinking Nautilus.

He told Denmark's TV2 there had been "a minor problem with a ballast tank … turned into a major issue". Ballast tanks hold water to increase the mass and therefore density of a submarine to allow it to submerge.

He said it took about 30 seconds for Nautilus to sink and he had not been able to close any hatches.

"I guess that was pretty good because I otherwise still would have been down there," he said.

He told police he had left Ms Wall in Copenhagen at about 22:30 local time.

A few hours later, early on Friday morning, Ms Wall's boyfriend reported her missing.

WHAT HAVE WE LEARNED SINCE THEN?

Not much.

The submarine was raised from Koge Bay on Saturday but Danish police said on Sunday that Ms Wall's body was not inside.

On Sunday local time Copenhagen police said, "it is true we have been given another explanation", but has not said what the explanation is.

A police spokesman now says there are indications Mr Madsen deliberately sank the Nautilus.

Sweden's Express newspaper reports that police have video surveillance films provided by Ms Wall's boyfriend Bo Petersen, who runs a restaurant near where she should have been released, but no announcement has been made about the content of the footage.

Before being arrested on Saturday, Mr Madsen announced via his lawyer he had something he would very much like to tell the press, but there has been no statement released.

The Express also reported Mr Madsen sent a text message to a colleague on Thursday night, before the Nautilus sank, cancelling a planned trip on Friday without explanation.