Released in 1973, The Crazies (aka Code Name: Trixie or The Mad People) was directed by George Romero with many of the same crew/production staff from his ground breaking feature Night of the Living Dead and has since been the subject of a Hollywood remake.
The plot plays out as an unknown, untested bio-toxin is released into the drinking water supply of a small Pennsylvania town after a military plane crashes nearby. The toxin causes strong, visceral reactions in those exposed as it creates an unrestricted id with extremely violent urges. The government storms into town, establishes martial law, and begins a round up of the townspeople. Some folks are understandably leery of the occupying force and find themselves caught between the infected "crazies" and the increasingly trigger happy "peacekeepers" sent in to maintain order. Screen time is also given to scenes illustrating the government/military's ongoing attempts to quell and localize the growing problem by any means necessary.