If nothing else, his prior "association" with Moussaoui was certainly the reason the FBI became involved after his arrest in Mosul. As someone else noted on this thread, his second trip to Iraq in 4 months was a red flag.
I guess with the password and Moussaoui, the Iraqi uncle, the odd jobs in Iraqi communications, his possible employers and acquaintances, his father's association with ANSWER, and the frequent trips, it would be more a surprise if the FBI wasn't keeping tabs on him.