Beyond Broken Pencils — Julie C. Gilbert

He has a goal and a plan. If he carries through with the plan, his sister will die first. His ex will die next, and he will die last. In between, he'll take out as many people as he can. Students. Security guards. Teachers. First responders. They are all fair game. Who will live, and who will die? How will those who live go on when their world is shattered by unthinkable tragedy?