The search for a missing reporter last seen on an amateur-built Danish submarine was set to expand into Swedish waters on Monday as Danish police said the vessel had been deliberately sunk.
The last hours of the submarine's final journey are key to an investigation into the disappearance of freelance Swedish reporter Kim Wall, who was last seen on the vessel on Thursday. Danish police confirmed Monday it was sunk due to "a deliberate act."
The police cited the results of a technical inspection of the wreck of the privately owned submarine, named the UC3 Nautilus, after it was recovered at the weekend.
The vessel sank Friday in the Bay of Koge, south of Copenhagen, shortly after its owner and designer, Peter Madsen, was rescued from it.
Undisclosed electronic equipment from the 18-metre submarine has been taken for analysis, a process expected to take some time, police said.
As part of their probe, Danish police were attempting to plot the submarine's movements from Thursday evening until it was spotted late Friday morning.
One lead came via a Swedish tabloid, Aftonbladet, which quoted a crew member on a freighter as saying their vessel had a close encounter overnight Friday with the submarine, near the Oresund Bridge, which links Denmark and Sweden.
The submarine was sailing without its navigation lights on, "something you don't do," the crew member said, citing the area's busy sea lanes.
Police said the submarine was heading for Sweden and was in the southern part of the Oresund straits at the time of the sighting.
Therefore, police were interested in "gathering information on vessels that have sailed through Oresund and the Bay of Koge" between late Thursday and late Friday morning.
A spotter aircraft was deployed in the search and Danish police also contacted counterparts in neighbouring Sweden concerning possible "support for a search of Swedish waters," citing the currents in Oresund and the Bay of Koge.
Swedish police were ready to assist "when we get a request," a spokeswoman for the southern Skane region told Swedish Radio.
Wall, 30 and from Sweden, was reportedly writing an article on Madsen, who has been remanded in custody after being charged with involuntary manslaughter.
Wall has not been seen since Thursday, when she and Madsen were spotted on the submarine leaving the harbour of the Danish capital, Copenhagen.

Via his attorney, Madsen said he will not contest a court order to hold him on remand over the disappearance of Wall.
But Madsen still rejects the charges against him, his attorney Betina Engmark Hald told Danish broadcaster TV2.
No body was found onboard the UC3 Nautilus when police searched it Sunday.
Police urged witnesses to report possible sightings of the submarine and Wall, and wanted to get in touch with previous passengers on Madsen's submarine in an attempt to establish where Madsen would sail.
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