The information in the following two excerpts from the NYT suggest to me there is no certainty about what exactly Moussaoui’s plea establishes as "fact."
Judge Rules 9/11 Defendant Is Competent to Plead Guilty
Published: April 21, 2005
" … Mr. Moussaoui, 36, attended flight training school in Oklahoma and
Minnesota in 2001 and received at least $14,000 in wire transfers from a
Qaeda operative who helped finance the Sept. 11 attacks, but he is not
known to have had direct involvement with the hijackers. Weeks before
the 2001 attacks, he was jailed in Minneapolis on immigration charges
after a flight trainer noticed that he was acting suspiciously. His
intended role with Al Qaeda has never been clearly established."
Surprise Terror Plea Leaves Unresolved Issues By NEIL A. LEWIS
Published: April 24, 2005
" … Mr. Moussaoui had demanded to question senior Qaeda operatives in
United States custody in secret locations abroad. He said they would
provide evidence and testimony to prove he was not involved in the Sept.
11 attacks, but rather in other plots not yet executed. The government
has resisted providing information from the captured terrorist leaders.
… Ms. Kayyem said that Mr. Moussaoui decided to plead guilty because
he understood that he could have been transferred to a military tribunal
if the government was unable to prosecute him in the civilian courts.