I recommend the movie "Zero Day" It's a film based on the killers of columbine high school days before they're massacre. The actors were really good in my opinion considering they were so young. If I haden't watched the behind the scenes, I would've thought the footage was real.

Another great movie I thought was good because I thoought it was real until I watched the bonus features was "September tapes". Based on september 11th and the war in afghanistan.

another good film about school shootings is Elephant. its original and shows multiple point of views which adds a pretty sweet effect