Which means
(a) he is a nutcase
(b) he had a couple more partners we haven't caught yet
(c) both a and b
My money is on (a). It doesn't seem like he is stable enough to have gotten too far in the planning process with partners.
As far as him being a nutcase, that's technically true, but I wouldn't read to much into it. For one thing, he's a Wahhabi fanatic and potential suicide bomber who was part of the largest terrorist attack in history, which supposed to trigger an apocalyptic struggle between Islam and the West. Take that little cornicopia of mental issues, and stuff him into solitary for three years, with the knowledge that his hijacker friends all are legendary in the Arab world. Plus, when he is executed by the corrupt courts of the great Satan, he will become the most famous Islamic martyr on the planet.
That spells 'nutcase' with a triple word score.
It's not at all unusual, though. While terrorist facilitators are quite sane and rational, they very often use the most twisted or broken of individuals in their plots. Some level of emotional imbalance, immaturity, or mental defect is pretty much required to be a suicide bomber, and in Iraq we found that was most often the case. I've seen some potential sucide bombers who were intercepted prior to their 'wedding', and they're not exactly the cream of society.
That fact that Moussaoui is mentally off kilter doesn't really suggest to me that he's not telling the truth. If he didn't make the first draft, then it may have been determined he was a little too off to pass unnoticed. That doesn't make him innocent in the least.