The conversation she remembers
with slight alteration
easily could have come out of "The Devils"
with Stavrogin as interlocutor.
After I made my previous post, I started thinking the same thing as you. Atta has consistently been described by many people as an unpleasant, threatening individual.
That's why I think the 09-11-01 letters were composed by Atta, himself. ("You die now", etc.)
His name is in the letters to NBC News and the NY Post (the highlighted A-T-T-A that it looks like he may have gone over repeatedly with his pen, as a "signature").