These "Mercenaries" are just police officers working undercover.
This is a common tactic used by the police in my country Sweden.
The Police use undercover police officers to quickly arrest the worst troublemakers in a crowd.
This antifa-guy gets arrested by 5 police officers, fast and clean.
https://youtu.be/9exPEj4rDro?t=221
Police arrest some kid in the street.
https://www.youtube.com/watch?v=SSp6n-wrvhE
Think before you post, don't spread FAKE NEWS