You asked in the OP, HOw Al-qaeda could have known(about the exercise)?
My answer is that they did not care. Why would they? Take the time to read the commission report and it is all there. The intel failures, the training, and the entire timeline. HOwever, maybe they DID know.
If you looked into the timeline of 9/11, you would also know that the airliners did not immediately contact anyone. (FAA) (no intel there)
This means, that critical time was lost from the time of the report of the hijacking until NORAD knew anything. (NORAD)
VP Cheney was I am sure in meetings (UNless Zawahari had a secret meeting nothing to gain here)
The agencies you refer to, the FBI since the CIA would never operate on US soil
were aware of the threats but did not stop the exercise because
there were no reasons to (your agencies) So, there is no need to infiltrate anyone because as a collective, they screwed up and 9/11 occurred without AQ needing any additional knowledge. However, please read on.
Now, as far as the 'little known terrorists', they were not and have never been. They are a highly funded organization with cells throughout the world. Please look up the name Ali Mohamed, or you can use this link. No bipartisan craziness in the article..good old wiki
en.wikipedia.org...
You see, they did not need to infiltrate because as you can read, they, AQ, have been infiltrating the militrayaround since 1998. This is the man that bought about all of the CIA is AQ rumors. So, to answer your question more directly....
they could have very well known....and had DARPA make them some flying carpets.



