He should and will get off. He's an idiot but there's reasonable doubt and the problems lay more with the system than with him as an individual.
He shouldn't have been a cop, too jumpy. The system should have stopped him yes, but it doesn't absolve him of his guilt and shouldn't remove any punishment he should be receiving. Do we blame driving schools or the DMV when someone does something stupid while driving? Maybe, if there is a pattern, but even then we'd still punish the bad drivers too.
He needs to go to jail. He killed someone because he heard a loud noise. If you can find some blame to lay on the "system" fine, lets look into it, but this guy shouldn't be able to walk away clear.