On the night of Sunday, an alarm was triggered at Mjällby school.
After the guards discovered the damage to the window, the police were also called to the scene, who suspected that it could be a bullet hole.
The incident is currently classified as vandalism and weapons offences.
- I cannot say whether the technical investigation is complete, but a preliminary investigation has been opened, says Thomas Johansson, press spokesperson.
There are no suspects yet in the case.
"Parents and children should feel safe"
Ragnhild Hellström is the principal at Mjällby school and she personally feels no concern about the incident.
She believes that if there was a threat image, she would know about it.
- This must not be allowed to take over, parents and children must feel safe.
I understand it creates concern, but I get angry the most, she says.
On Wednesday, it's time for students to return to school after the summer vacation.
According to Ragnhild Hellström, the police will be present at the start of school - but not to increase the feeling of security, but to investigate the incident further.
- I trust the police and know that they are doing what is necessary to get to the bottom of this.