ventlation system of a large building it could have devastating effects. so these risks are out there. whether this is connected with the boss ton marathon bombing or not. obviously at this point we don't know one way or the other. jon: one of the concerns obviously always has been some foreign state, a bad actor might conspire, you know, to do that kind of thing in our country. it is a question we'll get into if you can stick with us over the course of the break, mr. ambassador in a moment. more updates on the ricin attack that apparently found letters testing positive for ricin delivered, or sent to the white house as well as a couple of u.s. senators. back with more on that in just a moment.