Whilst this is a bit speculative, I would not be surprised if this was a case where criminal organizations in Sweden have been hired by the Islamist Ayatollah regime in Iran to perform terror attacks.

SÄPO (swedish national security police) has noted instances of gangs being used as terror mercenaries and previously during the year announced that they managed to prevent attacks.

Currently, the Swedish government is considering activating terror laws against the involved gangs.

Good riddance