The boy, a pupil at Slottsstadens School in Malmö, was arrested several weeks ago with two others on suspicion of planning to kill teachers and children, let off explosives and then take their own lives. His accomplices, who are said to be younger than the main suspect, were released - having admitted involvement - due to their age.
But the 16-year old denied the charges, despite the discovery in his home of what Aftonbladet called "decisive evidence". As well as a hunting rifle and "many chemicals which can be used for making bombs", police found a computer which contained detailed plans and times for the attack.
It is thought that the "massacre" was to be carried out on April 20th next year - the sixth anniversary of Columbine killings.
"Certain intended victims had been more clearly identified than others," said Caroline Aspinger of Malmö police to Sydsvenskan. "His computer has been very enlightening."
According to the paper, the boy has been in trouble with the police before and faces charges of robbery and assault, crimes said to have taken place in February. He is also suspected of forcing an underage girl to have sex with him and carrying out two burglaries.
"Everyone knew that he had weapons at home and that he was able to make bombs," said a former classmate to Aftonbladet. "He's dangerous - you don't want to be his enemy."
The prosecutor dealing with the case, Anders Pettersson, agreed.
"His plans really were very frightening," he said.
Frightening enough, in fact, to knock the story of a school knife attack off the front pages.
A 14-year old girl at St Olofs School in Sigtuna was stabbed in the shoulder at around 9am on Monday by a fellow pupil who fled into the forest near the school. The attacker, a boy of the same age, was later found by police. He was questioned and charged with serious assault - but the case will be taken over by the social services on account of his youth.
The girl was taken to Karolinska hospital but was later able to go home.
The headmistress at the school, Ulla Fahrman, expressed the shock of everyone at the school.
"We are all dismayed at what's happened here," she told Stockholm City. "We have never had a problem with violence. The school is in an area that could be described as idyllic and the boy is a very well-balanced pupil"