The officer without the gun properly holstered is one of the participants at fault. He did not have the gun set to standard operating procedures, and it went off on him. The officer who shot the boy was under the impression that the boy had a gun, and thereforeeeeeee defended properly (by shooting at him), and although this was an incorrect decision, there's no practical way for the officer to know that the other one had shot himself. Although it sounds mean, the second officer was just doing his job by defending the peace (if a guy shoots a cop, of course another cop would shoot back)
The kid is also at fault, for stealing a car. Crime has consequences, as he so violently learned.
Hope this helps,
WordYo23