Well, we don't know why the student did the killing. He was from the Eastern (depressed) part of Germany, and was expelled from school. It sounds like he felt that his life was over, and wanted to get even with his teachers. There are crimes that look like they were motivated by a wish for noteriety; this isn't one of them.

He had weapons (a pump action shotgun) that German law did not permit him to have. So the moral seems to be, there is a black market for weapons, a result of open borders.