The tactics are not sophisticated.
They are simple and obvious.
They have not happened before because there was good intel on organizations who might plan such an event. Under this President, collecting intell has been discouraged, radical anti-U.S. organization has been encouraged, and the demonization of the police has been pushed like no other president in history.
I was referring to the tactical operations of the shooters. Triangulating their positions to funnel the cops. Their movements during the operation. These are not just some random BLM thugs. These guys are pros.