If they had advance notice, why did they let it happen?
Maybe because they hadn't done anything yet. How many women have gone to the police terrified of some man and the police say they can't do anything until the guy actually does something - like murder them?
The PC morons will eventually give away their souls for a diversity goal of 7th Century barbarism which will ultimately be their tomb.
Yes, they had. The police had them on tape committing a conspiracy to attack the teacher. That's a world of difference better, legally, than someone calling the police and saying "so and so is threatening me." They also could have set up a sting to get them in the act before doing any damage but allowing enough of a confrontation to add the charges of assault and battery.