Why should it be any different of a response when a cop is murdered or joe blow citizen? Are cops more important than just us peons? Does the fact that a cop was murdered justify extra judicial actions? That is absurd.
I understand the human reaction that a cop might have in this circumstance, but they are suppose to be well trained and disciplined in the rules of law and procedures.
It's more that when the perp shoots at the cops, he shows he is a clear danger to them, whereas if he, say, shot his friend while playing poker and is now holding the wife hostage, he has not shown a danger to the cops.
That's just basic tactics. You treat someone shooting at you differently.