Is Putin a War Criminal?

More than one million people have signed an online petition calling for a special international tribunal to try the russian president and his closest allies. Such courts have tried and convicted war criminals from randa, serbia and elsewhere before. Once someone is called a war criminal, what happens? What sort of investigation does that trigger? The president calling someone a war criminal doesn't really make any difference. It's very unusual to say about a serving head of state, he's a war criminal.