That guy is a sadic. It's OK to be scared. It's OK to confuse a camera with a gun, and shoot before discovering that it really was a weapon the hard way. That shit happens at war.
But aiming a severely wounded guy, begging him to take a weapon so he can shoot without permission it's sadistic. That guy is a sadic. Now we can discuss if he was born sadic or just the result of careful training, but it's hard to deny, watching the video and hearing the conversations that he wanted to shoot, and was having fun, the kind of fun a hunter feels.
Of course the US Goverment, the Army, whoever, is to blame because covering the thing up. But that soldier is a murderer, no question about that.