from the NY Post HIJACKERS' CREDIT CARDS STILL IN USE excerpt: October 17, 2001 -- Credit cards belonging to the suicide hijackers continued to be used after the Sept. 11 attacks - indicating associates of the terrorists remained in the United States weeks after the kamikaze strikes, authorities said yesterday. The most recent charge on one of the cards came two weeks ago - a full three weeks after the terror strike - a law-enforcement official told The Post.
They have said several times that the FBI was aware of terrorist accounts that they chose not to freeze, for the purpose of following the money trail. They probably released this after it was clear that the card was no longer in use.