I am sad that you think so lowly of the Ukrainian people.
That you think among any 50 there would be some to carry out lynch murders, and a majority to cover that up.
Once again I'm reminded of the story of Ken McElroy. The people of a small town decided their local bully needed killing. So they arranged it, and then covered it up. Given what we know about the nature of his bullying, and the lack of response from the "proper" authorities, I don't think what those townsfolk did reflects badly on them at all.
I wouldn't begrudge Ukrainians a similar response, in a similar situation. Just as I don't begrudge the Americans their response, when they found Osama Bin Laden in Pakistan, and shot him in the face in his own home.
If Ukraine infiltrates Putin's personal staff, or sends commandos under cover of darkness, to find him where he lives and put an "extrajudicial" end to his life, I won't begrudge them that act, nor think less of them for carrying it out. On the contrary, I'd think less of anyone who complained that it wasn't "fair" or "humane" or "due process".
That said, I'm opposed to "killing by righteously indignant mob" as a formal method of execution. If the Hague were to turn Putin over to legitimately aggrieved Ukrainians, to dispose of him as they see fit in the depths of their grief and anger and desire for revenge... Actually, I may need to think about this some more.
ETA: I'm also reminded of that movie
tripe trope where Hero kills his way through mobs of henchmen, but stays his hand against the Villain, because he's better than that. My ninja, you've been doming conscripts using night scopes. You've been dropping grenades on wounded vatniks from drones. You've lit them on fire. You've watched them drown in shallow ditches because you've wounded them too badly for them to escape a puddle. You've blasted them with artillery. You've gone after them with tanks and bombs and machine guns. There's nothing you haven't done to vatniks a thousand times over, that you should refrain from doing to Vladimir Putin if you get him in your sights.
I fully expect Putin to go out badly. Most likely by his own hand, or by the hand of one of his co-conspirators. I expect his death throes to be nasty, brutish, and short. I won't feel bad for him, or guilty about my satisfaction, when it happens. And if he dies a horrible, lingering death from multiple health complications and inferior healthcare, I won't feel bad about that, either. And if by some miracle the Ukrainians are the ones to make it happen, I won't feel bad about that, either. Not for him, and not for the Ukrainians. But I think the Ukrainians are probably more concerned about driving Moscow out of Ukraine, than about getting Ukrainian assassins into Moscow.