I think the number is credible. They are not referring to traditional nuclear warheads. They are referring to dirty bombs, the way I read it.
Even then I doubt they would wait until they had more than a dozen. When lower Manhattan, central Washington DC and the Chicago loop are radioactive messes, who is going to care that Sioux City is too?
If they’re writing letters they either don’t have the bombs (dirty or fission) or can’t operate them (little different from not having them).
The only thing that worries anyone about threatening screeds is that someone is unhinged enough to write a threatening screed and should probably be removed from society.
160? 16? Heck, 6? Whatcha waitin’ fer, guys? CNN needs something to hyperventilate about! Talk is cheap. Detonating a dirty bomb would make history; threatening to makes the dustbin of history. They know this; that’s why I don’t believe the letters.
I agree, and low-grade radioactive material isn’t really that hard to come by. If I were the FBI, I would start by investigating any companies that deal with the repair or disposal of medical equipment. Some of those scanners can contain quite a lot.