This is a bit old, but check this out. I was recently made aware of this so it is new to me. The police of Quebec have admitted to sending undercover officers dressed as anarchist black blocs to a protest at which 3 undercover officers were exposed by union leaders. When pressed about the issue, the police department admitted publicly to the supposed black bloc members in question actually being undercover policemen, however, they claimed that they were only there to catch violent rioters in the act. This would make sense to me, however, what the fuck is one of the officers doing holding a huge rock??? Is that really a necessary part of his costume??? The only possible thing he could've been planning with that rock was to contribute to the violence. Check this video:
Along with this, a Minnesota sheriff admitted to a citizen at a town meeting that there were undercover officers present at the 2008 RNC, though he never stated that they were dressed as black blocs and he assured that his officers were not involved.
So my conclusion -- and I don't think anyone is surprised -- is that I believe it to be a high possibility that much of the violence committed by supposed anarchist black blocs at otherwise peaceful protests is really committed by cops who are at these events undercover dressed as black blocs. The intent of this is to not only discredit the anarchist movement, but to discredit protesters in general. And no one seems to give a shit. They spoke in this video, which is three years old, of doing something on a political level, but to this day no action has been taken, even on the very undercover cops that were exposed.