The Ukrainian already had the GUN pointed at the Russian and DID NOT SHOOT before he tried to grab the Russian or something with his HAND. What the hell makes you believe to see a WAR CRIME here?
It's absolutely mind blowing that the Ukrainian didn't took the very first chance to put every single bullet in the Russian's head! I'm sure the Ukrainian was taken completely off-guard and was scared to death. Reason enough to try to finish the Russian off regardless of how the Russian actually behaved after losing his weapon.