Is a person smiling and asking to take a selfie with you violent? These people are idiots who did bad things and should be arrested, but their bad thing was what? Criminal trespass? That's a violent coup? You exaggerate and it blinds you to the most likely explanations.
I am pretty confident that the police held them out of the building while it was evacuated, and let the barrier down into an empty building, because it was tactically the option with the least damage done. And with the exception of a single protester, I think it was pretty successful at that, at least so far.