Police suspect murder and have arrested one woman and two men, though not for murder, but rather for helping the criminal by making it harder for the investigation to take place.
A further three people have been brought in for questioning.
News agency TT reports that the police were notified that a row was taking place at the address, but when they arrived, they found nothing of the sort.
"It's still a little unclear what happened," says Ulf Lindgren of the Stockholm police. "But there was an injured person, so obviously, something happened there."