Ebbie is exactly right. In fact, Dylan Klebold wrote exactly such a story for his English cass at Columbine: it was about a guy dressed in black who took a lot of guns and started shooting jocks and other students. Then, a couple of months later he himself dressed in black, took a lot of guns, and started shooting jocks and other students.

Now, Dylan's story WAS fiction, and presented as such. While the teacher talked to him about the story, she did not take any disciplinary action.    In this case, the student CLAIMS the story is fiction, but then it's written in his journal, not where you'd typically write a short story. As others have said on this thread, we'll see what happens.