Who really did it is completely irrelevant in Russia, and something we will probably be never know.
The important thing is who do we SAY did it. How do smear this in a way that benefits us?
I'm 60% sure Putin ordered it some way or another. He's the one who benefits in the end, and his media will spin it in his favor. I'm also not sure many would dear to kill off politicians without his permission.
Don't think he cares about international rep anymore, just power politics and national standing. Ofc the conspiracy loving russians will love the most insane conspiracies, while ignoring the conspiracy that is most obvious. Anyway.. pure speculation.