I would think, they would be able to find he read ISIS propaganda and these are the kinds of attacks they were suggesting.
Tom what I see is a country and about ½ of its population and most of our politicians, Police Chiefs etc living in a state of Political Correctness called Denial.
Most of my adult life I have been in a position of authority and my days were filled with making decisions. Sometimes I had ample days to ascertain the facts, staff the action, get input and then make the call. But more often than not I had to make a 'command decision' in real time. I won't try to tell you that over my career I never made a mistake, I did and in almost every case it was due to a lack of qualified facts bearing on the situation. In this case I would be confident making the call...its terrorism and no one can put enough lipstick on this pig to call it anything else.
We need to thank that young policeman who double tapped the perp for making the correct decision in real time and not mistaking the perp for a Ginsu knife salesman...
https://www.youtube.com/watch?v=abLB7aTmnE4