Two women died at a high school in the southern Swedish city of Malmö on Monday in a violent incident, police said.
Police said the women were employed at the school and died as a result of acts of violence inflicted on them. They were both between 50 and 60 years old.
An 18-year-old pupil was detained on suspicion of murder. Police believe the suspect acted alone.
The Aftonbladet newspaper reported that the women were attacked with an axe and a knife.
Police had earlier spoken of a serious crime at the school. What exactly happened remained unclear Monday night.
The two deceased women were presumably the same people police earlier said were taken to hospital with injuries after several police cars and ambulances were sent to the school in Sweden's third-largest city.
Aftonbladet newspaper reported that the headmaster said he knew only that "deadly acts of violence" had taken place at the secondary school.
According to local broadcaster SVT, pupils were in the building at a late hour to prepare for a musical before police entered the building with guns drawn.
The school's principal, who was some 250 kilometres north in Gothenburg at the time, said all he knew was that "deadly violence" had occurred at the school, in comments to Aftonbladet.
Police later said they had the situation under control and some 50 people had been on the grounds at the time the crime took place.
It was unclear if the incident at the school had anything to do with the country's rampant gang crime, which has led to renewed shootings and explosions in cities across the country for some time.
Malmö has known about the problem of criminal gangs longer than other parts of the country and has taken several measures against it.
In particular the Malmö district of Rosengård - where Swedish football star Zlatan Ibrahimovic grew up - is considered a dangerous neighbourhood.