They actually focused on the foreign angle, and possible connections to the 9/11 hijackers. far more in the first month or so of the investigation. That the possibility of foreign involvement has been "ignored" is incorrect. They switched to focusing on domestic after they were unable to turn up anything linking it to foreign activity or the 9/11 hijackers.
What is your source for the 200 Taliban trained in Northern Iraq and, in particular, their subsequent movements?