This is a story that has been going on for some time.

It's useful when a group wants to prevent others from peacefully protesting an idea. Just send in a group of violent people to attack either the peaceful protesters in an attempt to get them to disperse or to start fighting among themselves.

Or, have a group join the peaceful group and have them attack police. This allows police to justifiably respond in force against the group who would otherwise have been peaceful.

Optically, this has the added benefit of being able to show footage of the peaceful protesters behaving badly.