Don't misunderstand my position. By no means am I defending the FBI nor the CIA. They have data bases filled with photos and bios of known terrorists in and outside of N.America. I don't know if you have many public security cameras but having been through American airports several times they are in plain view. Imagine the ones you can't see. The problem lies with these 2 security services communicating with each other. Both are very territorial the FBI is responsible for U.S. security and criminal investigation within the borders of the U.S., and the CIA watches foriegn nationals and spies on and in other countries, including Austrailia and Canada. They won't share info with each other, and this is the result. So to answer your question, yes and no. The would have checked the manifests and looked at known terrorists, and then cross-refrenced it with the data base of known operators inside U.S. borders. Unfortuneatly too little, too late. Many things occurred that day that probably won't ever happen again(I hope), mainly due to the knee jerk reaction. Regardless of what you hear in the news, I have flown into Boston and Washington for seminars in the last 6 months and the security now is extremely hard. Just a point of interest, I don't know how old you are or if you are a student of history, but this situation has occurred in the U.S.'s past. Pearl Harbour. Several people had advanced knowledge of both situations but the ability to step away from the situation and take a look at the overall picture(the big picture) and take all the info and try to formulate scenarios that may occur is easier said than done. If a complete stranger walks toward you on crowded street, quickly pulls a gun and shoots you, is it your fault for not being aware of strangers. We all were taught to be cautious of them, but can we really call it living if we walk around in utter terror all the time. This is how the U.S. used to approach threats. Now they follow the latter.