Lord forbid nobody caught the murder on video. This happens all over America, all the time. Thread is full of links or a quick hop on google will serve you in this regard.
What would have happened if it was citizens? All four would be in jail immediately, if they even get that far without being shot for "resisting arrest" first. At the very least they'd get a beating somewhere between having cuffs put on them and getting into a squad car. We know this from all the recorded instances of police brutality looking exactly as I've just described.
Lost their jobs. Come on. Would you merely "lose your job" if you watched your buddy murder a guy and stood there throughout the whole thing?