The police were alerted by SOS Alarm at 22.20 on Friday evening about a case of illness in central Stockholm.
Once at the scene, it was established that it could instead be a murder.
– It is the circumstances at the scene that make us suspect it, says Mikael Pettersson, officer on duty at the police.
The person was found dead indoors at an address in Vasastan. A man has been detained on suspicion of murder.
– He was arrested on the spot, says Mikael Pettersson.
The crime scene has been cordoned off and a technical investigation is underway at the scene. Investigative measures in the form of, for example, door knocking have also been ongoing during the night.