I guess you wanted him to behead the police officer first? Then there’d be cause to stop and question him?
If there was evidence of a specific attack, I would expect there to be an arrest warrant issued and the FBI/BPD show up with overwhelming force and take him down. That is how law enforcement is supposed to work according to the Constitution.
The FBI does not operate in a manner to show up and question a guy at 7 AM. They arrest the guy at 4 AM and show up with 25 agents to take him down, therefore preventing this.
I am smelling something fishy from LEO on this one