A person has been arrested on suspicion of breaking into Östragård prison in Vänersborg and leaving a bag believed to belong to one of the inmates.
The man, who is aged 25, is suspected of gross illegal trespass.
In connection with the incident, someone poured boiling water from one of the institution’s windows. The water landed on a police officer who was slightly injured and needed medical attention.
A notification of sabotage against blue light operations has been drawn up.
The incident occurred shortly before midnight.
Östragård is an open institution with 173 places. The inmates wear ankle shackles and are allowed to stay freely in the immediate area during the day.