A 17-year-old student is said to have killed his teacher in Ibbenbüren, Münsterland.
After the crime in the classroom, the young person dialed the emergency call himself and was arrested without resistance, said a spokesman for the public prosecutor's office in Münster on Tuesday evening.
The crime happened at a vocational college.
The suspect is said to have visited the 55-year-old in the school building in the afternoon, according to the homicide investigations carried out so far.
At that time, the teacher was alone in a classroom.
The investigations into the background of the fact are at the very beginning.
A larger police force had arrived at the vocational college on Tuesday.
In addition to several patrol cars, a rescue helicopter, an ambulance and an emergency chaplain also arrived.