incident taken place by guilty man with knife

Oct 5, a junior high school student(14 years old) was pierced with knife by a man(40 years old). Because some friends of the students witnessed the incident, a man was arrested. Although the student was in no danger of losing his life, no one can forgive the guilty person for his crime in any case. The student had no fault, and he was just walking with friends. What on earth did the man pierce the student? Is there any measures to stop these incidents like this?