Either the cops and the activists are feeding each other information or the cops have infiltrated undercover, this is how it works in the UK. I wouldn't be shocked if it were a similar setup in the U.S.

US local cops do very little undercover work so far as I know. What they do is busting prostitutes and drug dealers. I don't think it has a lot to do with politics. The main role of the local cops right now seems to be to stand down and get kicked around by black politicians.

But there are various other kinds of law enforcement that you probably have heard of that do the political work.