I suspect a lone nut at this point. I would imagine if it were terrorism, they would be now have sent out their manifesto, with threats of more to come—or at least we would be picking up that international chatter through NSA channels, etc..
Why? Who says it was a large cell or that Al Queda is going to warn America that attacks like these are coming? Until proven otherwise it is a terrorist attack. This is a very well planned attack like we have seen worldwide.
Pray for W and Va Tech