In order of appearance : Ben Coccio recalls that he was in a Brooklyn pizzeria on the day of the 1999 Columbine High School massacre , and saw coverage of the event on the eatery 's television , commenting , " I remember thinking that I was surprised that it had n't happened sooner . " Coccio was also struck by the extent to which Eric Harris and Dylan Klebold planned that shooting , compared to the impromptu crimes of passion that typified other school shootings . Coccio became eager to address the story in a way that was not exploitative , and drew upon his own views of high school as a place of tension where " anything could happen at any time " . Coccio 's theory of student school shooters is not that they are the most bullied , as such students tend to develop feelings of inferiority and are likely to harm themselves . Coccio feels that shooters tend to be students with feelings of '' superiority '' , and that " when other people do n’t confirm that , it really gets under their skin . " None of the numerous Connecticut high schools where he sought to film the movie would allow Coccio access , and he ended up using the interior of a building at State University of New York at Purchase in Purchase , New York . The " appropriately fortress-like " exterior of the High School was New Milford High School in New Milford , Connecticut , where Coccio lived at the time . When casting , Coccio inquired at high schools throughout Connecticut looking for teenagers interested in acting who might not have much or any professional experience . Coccio had three days of open auditions . Andre Keuck responded to an ad Coccio placed in Backstage Magazine and brought his classmate and fellow theater enthusiast Cal Robertson along to the audition . Both boys had acted in Shakespeare productions at the Stratford Avon theater in Stratford , Connecticut . They were encouraged to improvise throughout the film 's production
Columbine High School massacre
Columbine High School massacre
Zero Day (film)