I'd like to see that. Why don't you go ahead and tell people that Putin is too nice a guy to be involved in killing people? Tell people what you know about him in that regard.
Meanwhile, don't let Putin's laughing at you bother you. You go right ahead and tell people what you know about Putin that convinces you he's too nice a guy to kill people.
The first principle of debate is “he who asserts must prove.”
All I can say is that I have researched on the internet every one of these alleged “Putin murders” that I have come across and have not found credible evidence to back any of them up. In nearly all cases, the murder in question harmed Putin in public opinion more than it could possibly have helped him (and whatever you think of him he is a smart man and smart enough to know that) and/or that other elements including Russian mafia oligarchs, or others had much better motives than he had in the individual case.