You still seems to believe that they're competent enough to create believable "unfortunate accident". The point of using nerve agent is that Kremlin believed it

You still seems to believe that they're competent enough to create believable "unfortunate accident". The point of using nerve agent is that Kremlin believed it to be untraceable. It's very much opposite of polonium. Obviously it's just my view, but to give you an example. Nemtsov was one of old Russian political leader who been neither popular nor real danger to regime end up just shoot right in front of Kremlin. And it's caused a lot of backslash and place of his death is still PITA for Putin regime. Navalny is more popular by two orders of magnitude at least. On top of that everyone know that he's being watched literally 24/7. If he die in suspicios car accident or something like that it's might actually trigger a lot of bad things or might finally put some real beneficiaries of regime (like oligarchs, kids and other family members) under sanctions. It's not that hard to get someone killed in Russia, but really this is not Stalin's totalitarian country and no one want risk losing all their capital and property in western countries. On other side anyone can die of heart attack during flight and it's impossibly hard to prove it was poisoning afterwards.