The man was one of a group of four men arrested in Kalmar on drug charges on Tuesday, Barometern reports.
The man was detained at Kalmar police station to avoid overcrowding at the nearby remand centre, which was already full.
“From what we understand he hanged himself from the toilet door with a piece of cloth,” police spokesman Sven-Erik Karlsson told the newspaper.
Police said they performed the same suicide assessment at the station as the would have at the remand centre and came to the conclusion that the man was not likely to injure himself.
He was left alone, only coming into contact with the guards when he requested their attention.
Shortly before 8pm he asked a guard for permission to use the toilet. By the time the guard returned the man had already taken his own life.