The commander was arrested in May on suspicion of using a false document, a felony.
The preliminary investigation has also been closed because there is not enough material to prove a crime.
The Sea Owl had initially been given the go-ahead to leave Trelleborg, but the vessel turned out to have been falsely reflagged. Earlier documents said the vessel was registered in the Comoros, but it was later reflagged to Cameroon.
The Coast Guard has previously announced that the ship is on the EU sanctions list and that it has been transporting goods between Russia and Brazil.
