The Crazies (1973) DVD

A military plane carrying a secret bio-chemical warfare agent crashes near Evans City, Pennsylvania, releasing a deadly virus into the local water supply. Highly contagious, the virus quickly begins to infect the town's residents, producing homicidal insanity in its victims. As government scientists work to find an antidote, the town is forcibly quarantined by the US military. Clad in protective suits, troops of soldiers move in intending to control and cover up the situation, and to prevent the further spread of the virus. However, local resistance to the heavy-handed military presence soon leads to widespread panic, rioting and murder. 

Meanwhile, a group of seemingly uninfected locals, led by a former Green Beret, are plotting to flee the town...