Staff at Norrköping prison said that the hash probably wasn’t intended to hit the guard.
But so far none of the prisoners had staked a claim for the airborne narcotics.
“A lump came out of the sky. It was just less than a hectogram (3.5 ounces),” said police spokesman Lars Engström.
Police scoured the area around the prison but were unable to find the person who had thrown the marijuana missile.
The guard did not require treatment for the lump on his head.