Just before 7 o'clock, the rescue service issued an alarm about a car fire in Storvreta.
It was during the extinguishing work that the rescue service and police found the three dead people in the car.
A large area has been blocked by the proximity of the sports ground Skogsvallens IP.
"We do not know anything about how they have died, but we suspect there is a crime behind and have therefore initiated a preliminary investigation into murder," police spokesman Daniel Wikdahl told TT.
According to the police, the people are not yet identified and it is not known at present how they have died.
- We are still at an initial stage of the investigation. It's about catching witnesses and hearing people in the area. We are also working on tracking and searching the area to hopefully find out what has happened, says Daniel Wikdahl to TT.