The thieves first used trucks to crash through protective fencing surrounding the trailers in the early hours of Sunday morning.
They then hooked up the trucks to two trailers before speeding off with goods police estimate had a value in the millions of kronor.
“It was a very sophisticated job and the goods were of a particularly high value. They knew what they were after and there’s reason to suspect this was an inside job,” said Gothenburg police spokesperson Per-Arne Nilsson to the Göteborgs-Posten newspaper.
It’s the second time Stena has been hit within the last month.
The company updated security procedures following the first robbery, something which Nilsson believes caused the burglars to take a more direct approach at the weekend.
“Stena tightened procedures and that’s probably why they drove right through the fence this time. Stena has done its best to protect the freight, but the thefts are so well-planned and well-organized that it doesn’t help,” said Nilsson.
According to Nilsson, the number of thefts of goods in transport in southwest Sweden has decreased from 468 in 2007 to 239 so far this year.
At the same time however, the value of the goods stolen has doubled, leading Nilsson to believe that highly organized criminals are responsible for the heists.
A spokesperson for Stena Line, Joakim Kenndal confirmed the thefts but wouldn’t comment on the content of the trailers that were taken or value of the stolen cargo.
He added that he had never previously heard of thieves stealing Stena trailers by driving straight through the perimeter fencing.
“We now need to review our surveillance system further,” he told the newspaper.