This is precisely what I was worried about in my previous post on the polonium incident.
I am somewhat more sceptical on the politics and the science is light but definitely something to worry about. He is right on the money.
There is something wrong with the "assassination" theory. Polonium just isn't a good way to do something like that.
As far as the dirty bomb blow off he is somewhat right in that death tolls would be very low. On the other hand for a year or so no one could go within a mile of the site without some risk of pretty nasty polonium poisoning. So even if it isn't a nuke it would be pretty bad and very public.