Remember this is all situational. I imagine the FBI gets hundreds of tips daily but can't act on all of them without enough mounted evidence to take it seriously. They may have had tips earlier of the attack but they couldn't verify in time.
It always looks worse when you view it in hindsight. If the FBI had enough evidence to work with then they would have done something. Acting early without the evidence they need would have done more damage and not necessarily stopped anything from happening.
It always looks worse when you view it in hindsight. If the FBI had enough evidence to work with then they would have done something. Acting early without the evidence they need would have done more damage and not necessarily stopped anything from happening.