Many real aspects of Columbine shooters Eric Harris and Dylan Klebold were used in the film. Most obviously being that the entire film was shot exclusively as a video diary (excluding the massacre itself), as Harris and Dylan did film many videos (later known as "The Basement Tapes") documenting their plan. As of October 2014, "The Basement Tapes" still have not been made available to the public.
No professional film cameras were used in the making of the film.
During the scene where Calvin and Andre go shooting with Chris, Andre says "Natural Selection" while Calvin is firing. "Natural Selection" was Eric Harris's (Columbine shooter) favourite law. basically, it states that nature gets rid of the weak organisms, while supplying the stronger organisms.
Like Andre, real life Columbine Massacre assailant Eric Harris worked in a pizza parlor, as did other Columbine assailant Dylan Klebold. And like Calvin, Dylan Klebold attended the school prom just prior to the massacre.
Andre an Cal's parents were portrayed by Andre Keuck and Calvin Robertson's real parents. Director Ben Coccio wanted the movie to be as realistic and believable as possible.