That wasn't my point. Here's a guy who says he wants to carry out violence. Later, he actually goes on to carry out violence.
My point is that you are insistent in minimizing the severe harm potential of the mob involved in this event. Reading your comments, I get the impression that you think that it was not reasonable to believe that this mob would continue carrying out violent actions; or (less likely) that, even if it is obvious, in retrospect, that this would have been the case, it is something that no one could have foreseen during the time when it was actually happening. Either of these positions is absurd.
Not all mobs are equal. Not all mobs have the same stated & unstated intents. Not all mobs are announced in advance with people who are to form such a mob saying that they intend to do bad things. Not all mobs are the same size. Not all mobs are advancing toward congress in session after being prompted to "fight" by their religious cult leader.
In this case, we have one such mob saying that they wish to do a variety of violent things and also doing a variety of violent things. One would be reasonable in supposing that a high likelihood existed of this mob doing more violent things if put into a situation where doing said violent things was an option for them.
It's not that difficult.