Det. Jeffries: Killer kids... first this, then Columbine.
Although in the show's internal world the events in this episode took place before the Columbine shootings, the plot is actually heavily inspired by the April 20, 1999 events at Columbine High School in Jefferson County, Colorado. Two high school students went on a shooting spree, killing 12 students and a teacher, and wounding 24 others before committing suicide. There is even an unsubstantiated theory that a third shooter might have been present -- just like in this episode.