So I'm watching (watching!) This American Life, and the intro part is about these science types who isolate a chemical that lets you store memories. Apparently, and the details are brief, when the chemical is blocked, rats lose all their memories. Like, all of them.
The scientists get published, and then get a bunch of letters from ptsd sufferers who want their memories erased. The scientists were a little freaked out, on account of they were just doing research, like to know stuff, and people thought, hey! we can use that!
So what if we made a chemical weapon out of that? Bomb a city, and all the citizens just completely forget everything ever. Like what a sink is.