And to comment on that earlier post, nuclear materials are far too difficult to manufacture, transport, and smuggle.

Consider something infinitely more concealable, cheaper to construct, and potentially more fatal. Bio-weaponry.

A 2 oz shampoo bottle can contain enough virus or bacteria to wipe out 10% of the population. I think there was an old movie "Outbreak" that demonstrates how quickly something like this could blossom out to a national disaster.

Also, look up "operation dark night". Simulated war game involving a few janitors spraying a virus on plants in a shopping mall. To summarize: we failed miserably and the heath care system collapsed. 84% infection rate nationwide within 15 days, with a 60% mortality rate.

I could see someone doing this almost as much as I can see someone blowing themselves up. They don't care what happens to us after they pull the trigger. Their "cause" is chaos.