NY Times article reports no pre-existing damage found <a href="http://www.nytimes.com/2002/01/05/nyregion/05CRAS.html" target="_blank">here</a> (You may need to register for free to see this article).
According to the article, the investigators are now focusing on pilot inputs (and likely flight control system responses along with how that loads the structures).
It sure looked a lot like pre-existing crack propagation to me from the pictures, but if the fractures are shiny (or whatever you see in a fresh composite fracture) all the way through, it's an overstress.