The Mossad sent a top level delegation to the CIA four weeks before the attack and told the CIA that Bin Laden's organization was about to pull off a major attack on the U.S. that would involve about 200 of bin Laden's agents. The Mossad could not tell the CIA exacly what was about to be attacked. The French intelligence agency gave a similar warning to the CIA.
The Mossad's warning was apparently totally ignored by the CIA, the FBI, or both. Now the CIA is covering its tracks over this matter. And it is getting lots of help from the major media. The fact that the CIA was warned by the Mossad and by the French that something very big was about to come off has been completely squelched in all media discussions of the massive intelligence failure that took place.
Fact is our intelligence organizations stop dozens of attacks a year. Some are bound to get through. Instead of second guessing try supporting them. These guys have a really tough job to do. They pick of bits and pieces of information from all over the world and have to try to figure out what's going on. There's hundred of various terrorist organizations they're monitoring, each of which is working on multiple plots. Our intel guys have to match the info with the group and the plot and try to figure out who wants to make what go boom, how and when. To understand intel analysis do this: buy 100 puzzles, make sure they are all the same type of scenes but different scenes, make sure they're all at least 500 pieces, now take a fist full of pieces out of each box throw them on the floor, burn the boxes and all the remaining pieces, now take that pile of random fist fulls and tell me what each puzzle is a picture of. That's what these guys get to work with, random bits of information where step one is figuring out which "picture" it goes to, then what the picture means, and they have brutal deadlines.
We should be thanking these guys, we should thank them for their miraculous success rate. It's truly amazing how many of these things they stop.