Russia wants to execute people who volunteered for the Ukrainian army? Then their paid Wagner Group and Chechen mercenaries who’ve been captured by Ukraine will likewise require a trip to the gallows.
More likely he is there to address the Ukrainians using civilians as human shields and cannon fodder. That’s the real war crime.
Ukraine has been killing Ukrainians who don’t want to fight. When many knew the war was coming, many Ukes left Ukraine before being forced to fight.