This is starting to look more and more as if it could have been an attempted jihad "martyrdom operation."
Here's an excellent video link (thanks to Steve) to an Oklahoma news story on how Joel Henry Hinrichs tried to buy the same fertilizer used in the 1995 Oklahoma City bombings, and attended a Norman mosque -- the same mosque attended by "twentieth hijacker" Zacarias Moussaoui. He also had a Pakistani roommate.