One of the things that is puzzling me a bit is why whoever is using a Soviet era poison. Someone on the radio was saying if it was some stolen in the USSR era it would have lost some of its effectiveness due to age. No idea if that is true, and it is quite possible that effect would be smaller if it was kept in 'ideal conditions', but it seems a bit odd if they manufacture today something old and traceable, rather than something more up to date and less detectable, and I am sure such things exist.   The only good rationale would be deniability, as far as I can see.