How did these attacks happen?

The United States of America have a formidable amount of intellegence and security agencies. They have the CIA, the FBI, The DIA, The NRO, The NSA, the Secret Service. These particular agencies use Echelon, which monitors electronic communication; Tempest, a technology that can show what a person has on their computer screen a mile away; Carnivore, which intercepts email; Satalites that allegedly have a resolution of four inches, and loads of other spy technologies we haven't even got wind about. With all of those resources, all of the hi-tech wizardry, all of the intelligence agencies, The U.S.A. didn't even have the foggiest idea of a terrorist attack, never mind the hijacking of four airliners, and crashing them into famous landmarks as they did on the 11th of September 2001.

It just makes me wonder. How could the U.S. government not know there was an attack coming? Has their vast intelligence network become complacent...nay, completely imcompetant not to pick up on the attacks? Did the terrorists not use any sort of electronic communication? Phones, email, computers?
I argue that the intelligence community had some idea of the attacks. It'd probebly be bad press if they admitted they had a tip off but they didn't take it seriously enough to warrent further investigation. Or perhaps...well, it could be more sinister if ya wanted it to be.
Anyone wanting to provide some insight?

It's called Institutional Arrogance. Everyone KNEW that the US is the most powerful nation on earth and no one would attack us. Everyone KNEW that we'd kick the snot out of anyone that even TRIED to hit us, and we'd know all about it before it happened.

Originally posted by Zaphod58
It's called Institutional Arrogance. Everyone KNEW that the US is the most powerful nation on earth and no one would attack us.

BS. Your signiture says logic is dead long live BS. This above statement isnt very logical. Where were the fast movers dude? I dont gaive a damn what the government says they ALWAYS go up for a hijacking, if anything but to find out if they are haveing mechanical failure or if its really a hijacking. Dont tell me we didnt have aircraft in the area because we did. They would have been on flight 77 the second it went off course, holy moly we were attacked twice and you are trying to state we were arrogant? Someone made the desicion to stand down.

Prove it! How are you going to have a fighter on a plane "seconds after it goes off course" when you have TWENTY ONE FIGHTERS for the entire freaking country?! They're not going to send up an unarmed fighter that is completely incapable of doing anything for a hijacking. Even at the HEIGHT of the Cold War when we had HUNDREDS of armed fighters we wouldn't have had one on a hijacking immediately, because NORAD doesn't have an automatic launch procedure like everyone claims they did. They don't respond until the FAA notifies them.

I think the OP answered his own question. We had all this high tech wizardy ready to protect us from the soviet union. But we never considered low tech terrorists who relied on the most basic of technology.

Seems NORAD isn't aware of its magical capabilities, not only it thought the scramble takeoff time prior to 0911 was set to 15 minutes (actually the scramble jets at Otis went in 6 minutes but only because they were already put into Action Stations status).
As well NORAD isn't aware it could've seen the mainland of USA and thinks its radars covered just the ADIZ over oceans...
Also it thinks the FAA has to call DoD for scramble fighters and DoD then has to call NORAD to scramble some of the 21 jets from 7 bases all over the USA...

To respond original topic, Zaphod has a legitimate point and another problem would be amount of information where the real intent may be well hidden.
My favourite comparison is the D-Day and German Abwehr. The Germans knew exactly what to look for, they knew coasts suitable for large landing, range of Allied fighters, weather... But anyway they weren't able to get a warning. Now, US agencies were looking for action by unknown means, by unknown people etc. - ie they were in much a worse situation.

I've just discovered some really odd information.

I will post later...