Look I know there is a section of the hell-yeah Yankee-doodle neoliberal Mothers apple pie brigade who like to stick their tongues up Vladamir Putin's a$$ because he happens to be fighting against the new American boogeyman ISIS, but the simple fact is he's fighting the Muslims for HIS benefit, not yours. The man is still an autocratic dictator who plays upon the fears of the Russian populace to keep himself in power. And nothing plays upon fears more than this kind of thing.
Either the Russians carried out this hit, or some of their Agents have gone rogue and carried out this hit, or someone they have sold or given this stuff to has carried out the hit, or they've lost or had it stolen by someone. In any of those eventualities, they have some questions to answer.