The disease:

The disease originally spreads because of starvation. Namely because animals have taken in radioactive material such as folage and other animals that were perhaps caught in a fall out of sorts. People eat the animals and the disease sets it for some of them more quickly than others, the incubation period really unknown. The disease looks a bit like leprosy and tears down the humans ability to reason properly, which quickly aggregates into aggression, rage and a lack of morality. 

Because the incubation period is different, we will assume (IC) that all victims that began showing the signs of being mentally incapacitated, like on the acid trip you mentioned are going to get the disease, but perhaps they don't. I'd like to throw in that people having varying degrees of immunity to it that will need to be studied based on the illnesses that they've encountered in the past and have an immunity built up to. So like if you've had chicken pox, perhaps you only get the acid trip scenario here and there. If you have asthma or a pulmonary disease, it advances the illness and turns you into a zombie in a matter of weeks.

We could totally flesh out the details of the what and how IC with the scientist and her experiments. It would be fun to massage that one as we go I think. I like the idea of sending the "mob" or something else after the individuals that have the first symptoms, the acid trip scenario. I could have her (the scientist) have a very different understanding of the disease and be completely against killing anyone that isn't at the zombie stage, but the make-shift military coup or Marshall law situation has people not caring about anything but removal for these individuals. Fear is the ruler of the day and no one is willing to take a chance on the person going from loopy and carefree to eating someone's face off and spreading the disease further.