It was on January 28 that a 25-year-old man entered Peder Skrivare's school in Varberg, armed with a knife and ax and slightly injured a student.
The 25-year-old is in custody on probable cause on suspicion of preparation for murder, preparation for aggravated arson and for assault and aggravated unlawful threats against two people.
Several Molotov cocktails have been found at the school.
It has now been established that the man acted alone.
Posted posts from the school deed in Trollhättan
Just hours before the attack, the 25-year-old made several posts on Facebook - including one about the school act in Trollhättan in 2015.
District Attorney Henrik Kindlund has now taken over the preliminary investigation.
He says, among other things, that they map the man's preparations and that they also look at the information about what he shared on social media.
The man must also undergo a psychiatric examination.
The man has previously served a prison sentence for arson.
In the clip above, chamber prosecutor Henrik Kindlund tells more about the investigation.