A 55-year-old man died on Sunday morning after police found him severely injured in an apartment in Märsta, north of Stockholm, and a man in his 30s was arrested on suspicion of murder. Officers were alerted at 11.23 after reports that included shouting from a multi-family building in the Sätuna area, and the case is now being handled as a murder investigation.

Police and ambulance crews tried to save the man after patrols reached the apartment, but the efforts were unsuccessful and he was pronounced dead. An ambulance helicopter was also sent to the area, then left without taking a patient.

The arrest gave investigators an immediate suspect to question, and police have also deprived one additional person of liberty to be heard as a witness. Daniel Wikdahl said officers believed that person had a role in the incident, while making clear that the person is not suspected of any crime. The deceased man's relatives have been informed.

Police have cordoned off the scene and are continuing with technical examination and interviews. They say the case is being treated as an isolated incident and does not appear to be linked to other crime, even as the death itself remains under murder investigation. That leaves the key question unchanged for investigators in Märsta: what happened inside the apartment before the shouting, the injuries and the arrest?