When you think about it...
It's surprising this is as rare as it is.
I was amazed after 9/11 that this kind of crap didn't happen all over the place. I got ribbed here for taking a geiger counter with me on 4th of July after 9/11, but I figured a very likely attack would be a dirty bomb in places like Reno I would be traveling through.
Credit should also be given to FBI and others to many lots that have been thwarted.