It was on Thursday morning that the man entered the area of Peder Skrivare's school in Varberg, armed with a knife and ax.
There, he attacked a student who was slightly injured.
Before the man went to school, he is suspected of having started a fire in a garbage room nearby.
A preliminary investigation was initiated and the man was notified of suspicion of the following criminal classifications: suspicion of aggravated assault, aggravated arson, aggravated unlawful threat, preparation or attempted aggravated assault, and preparation or attempted aggravated arson at school.
Now the decision to detain has been made.
The school was closed after the incident and was also closed on Friday.