Whered did the terrorist get the gun? Was it legallly purchased?
Now that you mention it, I don't believe they ever report where a criminal or terrorist gets their weapons from.
Washington state is actually pretty reasonable about guns and weapons. I can load my Smith and Wesson .40, and have it sitting on the seat next to me, or on the dash, whatever. As long as it is in plain view.
Lotsa folks east of the mountains have gun racks. Few of them empty.