Something to do with Wallace and Nixon would be a very good place to start.
Doing this is possible, but it's going to take a few decades to fully implement, depending on where you start. More likely than not, the only way you can get Death Squads to come about is through rampant racism and reactionaries, combined with a Depression worse than the first one. Continued for years on end. The only real way to start is to create a TL that is just generally a dystopia and then working from there.