A group of black-clad masked men boarded the ship and, claiming to be police officers, searched the Maltese-registered vessel which was laden with timber bound for Algeria.
The vessel's Russian crew were bound and gagged for the duration of their 12 hour ordeal which began at around 3am on Friday July 24th.
The Swedish National Police Board (Rikspolisstyrelsen) have stated that the men were not police, neither were they representatives from any other authority.
"It is the first time I have ever heard of such a thing in Swedish waters," Ingemar Isaksson at the board said to the TT news agency.
The Swedish police were informed of the hijacking via the Russian authorities through which the 15-man crew had contacted the Russian embassy in Stockholm.
The Swedish police have launched an investigation into the hijacking amid allegations that the crew were assaulted with rifle butts.
Exactly what the hijackers, who spoke English, were looking for remains unclear. Reports indicate that they said something about a "drug enforcement control" and that they were looking for narcotics.
The Swedish police are in possession of information forwarded by the shipping company to the Finnish police but have not yet managed to contact the vessel.
Police are now making attempts to contact the vessel and are also appealing for information from any recreational sailors who may have seen anything.
The hijackers are reported to have been travelling in a high-speed inflatable boat. After the attack the vessel continued on its journey.