Alexander Litvinenko's death [1], on British soil, was definitely murder, though. According to the investigation, the Russian state was involved. Obviously, Putin didn't actually do the deed himself, but it seems more likely than not that he ordered it, or at least knew about the order.
Right -- No one disputes that Putin has been associated with all kinds of unseemly stuff. It's just that, at this juncture, there nothing beyond pure speculating tying him to Mikhail Lesin's untimely demise.
In other words: "He's a bad guy you know -- he's capable of anything" isn't, in my book, sufficient reason to believe that he was actually involved somehow.
[1] https://en.wikipedia.org/wiki/Poisoning_of_Alexander_Litvine...