Everyone knows Putin did it, just as he murdered journalists. They just don't care, there will never be anyone brought to justice in Russia.
putin has nothing to do with the journalists' murder or litvinenko. either some fringe kgb group got carried away or someone else (oligarchs, mafia, warlords, gunrunners, you name it, russia has lots of badasses to offer) got rid of people they deemed dangerous to their operations. those journalists were nobodies in russia, there was absolutely no need for putin to kill them publicly.
the kgb, just like the cia, the mossad etc., doesn't poison openly for the world to see but makes people vanish without a trace. that's the essence of secret services
. to me there's a higher likelihood that people like abramovich or berezovsky are behind the open hits we're witnessing related to russia.