Assuming this is a true account of the incident, he talked himself into a trial. He has described a situtation in which the enemy stopped and complied with his orders, thereby demonstrating that he had control over a surrendered enemy soldier. I think this guy may be in deep trouble. By talking about the incident he gave his superiors no choice but to investigate and maybe prosecute.
Maybe, but "ordered him to stop and forced him to turn around" is not the same thing as he stopped and turned around as ordered". He may have caught him, but he was still struggling and tried to get away after being forced to turn around. It will come out in the investagtion and and before any courts martial. I'd bet on no courts martial, but one never knows.
Did they find the bodies? Any corroborating evidence? Unless authorities can find corroborating evidence, a bare admission or confession to the killings will not sustain a conviction.