Ed's not just stating the obvious.
The need to establish blame, as in your scenario, is about worthless a trait as it was after 9/11.
The goal should not just be to find individuals responsible for allowing attacks to occur, but to Identify the "systemic failures" like the ones highlighted by the 9/11 commission report.
Failures in interagency communication as well as failure to adhere to existing policy in the case passport processing are holes in the dyke that hopefully have been plugged.
Dealing with terrorism at home clearly involves a learning curve. Sadly the price of education is very high.