Few facts are known about events on the Arctic Sea
By Penny Spiller
It has been a mystery that could grace the pages of a thriller novel.
A cargo ship carrying timber worth $1.8m (£1.1m) from Finland to Algeria is apparently briefly hijacked off the coast of Sweden before continuing its journey through the English Channel - and then disappears.
Nothing was heard from the Maltese-flagged Arctic Sea from its last recorded sighting on 30 July until Russian authorities said they had located the ship and its crew on 17 August.
If this event had occurred in the seas off east Africa, the finger would immediately have been pointed at Somalia's notorious pirates.
But the Arctic Sea disappeared while rounding the west coast of France, in what are considered to be the pirate-free shipping lanes of Europe.
And as the maritime hunt to find the 3,988-tonne vessel comes to an end, speculation is rife over what might have led to the Arctic Sea's disappearance.
Was the ship carrying something other than timber, "something much more expensive and dangerous", as one expert put it?
Or was its disappearance down to some commercial dispute or even a quarrel between rival Russian mafia gangs, as other observers have suggested?
From the outset, all the experts appeared to agree that the ship could not have sunk, as floating wood or oil would have been seen. But they also said this was no typical hijacking.
The Arctic Sea, carrying 15 Russian crew, left Finland on 23 July bound for the Algerian port of Bejaia.
A day later, in the Baltic Sea, the ship was reportedly boarded by masked men who claimed to be Swedish anti-drugs police. They tied up the crew and searched the vessel, apparently leaving about 12 hours later.
These events were reported to the Swedish police in a round-about way.
A police spokeswoman told the BBC that the ship's crew first alerted their shipping company to what had happened. The firm then informed Russian embassy officials in Finland, who contacted their counterparts in Sweden, who informed the Swedish authorities.
The police spokeswoman would not comment on any alleged drug link to the ship, saying only that no line of inquiry could be ruled out.
The facts about what happened remain unknown for now.
But, speaking before the ship was found, David Osler, who writes on maritime safety for Lloyds List, said speculation about a Russian dispute that got out of hand was plausible.
"It doesn't look like it's the sort of theft of a high-value ship or high-value cargo
so the longer it goes on, the more it looks like some sort of dispute between Russian interests," he told the BBC's Today programme.
Mikhail Voitenko, editor of Russia's Sovfracht maritime bulletin, went one further, to suggest "the vessel was loaded secretly with something we don't know anything about".
Also speaking while the ship was still missing, he ruled out drugs or "illegal criminal cargo", adding: "I think it is something much more expensive and dangerous.
"It seems some third party didn't want this transit to be fulfilled so they made this situation highly sophisticated and very complicated," he told the Russia Today news channel.
He pointed out that the unknown cargo could have been loaded in Russia's Baltic Sea enclave of Kaliningrad, between Poland and Lithuania, where the ship underwent repairs before picking up its cargo in Finland.
Such speculation was dismissed as nonsense by the director of the ship's operating company, Solchart Arkhangelsk Ltd.
Nikolai Karpenkov said the ship was checked by customs agents both upon leaving Kaliningrad and also in Finland.
His deputy, Ivan Boiko, told Russia's Itar-Tass news agency on Friday that the crew were highly skilled and came from a town "with long-standing sea-faring traditions".
He said there was enough food, water and fuel on board to last until September, when the ship was due to return to port.
Mr Boiko explained that Solchart Arkhangelsk Ltd had operated since October 2008 and "co-operates" with Helsinki-based Solchart Management, which organised the Arctic Sea's journey.
The ship, he said, is registered in the Maltese port of Valletta.
Malta's maritime authority was leading the hunt for the ship. Russia drafted in all its vessels in the Atlantic to help with the search.
The Arctic Sea is equipped with an automatic tracking system, but this appeared either to have been switched off or to have stopped working after its last signal on 30 July.
Based on an estimate of its speed and the distance it could have travelled, experts did suggest that the vessel could have ended up in waters west of Africa, where the Russians appear to have found it.
But burning questions still remain: how did it get there, and what happened along the way?