Books about school shootings (both fictional and nonfiction)

So I've had this strange special interest in school shootings for about a year or so, and I've been on this adventure to read every book and watch every film I can get my hands on about school shootings, and then give my thoughts on all of them.

So far I've read Dave Cullen's book on Columbine, and have also read Peter Langmans book Why Kids Kill. If you have any recommendations, please drop them here! I'd also love to talk about these books with some of you guys :D