Some more news on the Polonium Poisoning.
This might lend additional credence to the argument that this was a mistake in transportation vs. a poisoning attempt.
If he was repeatedly receiving the shipments exposure could have returned multiple times.
One other item on this hypothesis is that Polonium has some interesting physical characteristics in that it will "climb" the walls of a container that it is in and passes weak seals easily. (only is significant quantities)
It does call into some suspect the Chechen link though.
Think hyper mercury.