In most cases, murder is something that happens in the heat of the moment, and usually to someone who knew the victim. Even in most cases of robbery, the perps usually don't plan to actually shoot, but do so when something triggers a fight/flight response in them. This isn't meant as an excuse, just an explanation. When a violent career offender kills a cop (plus the K-9) in an attempt to flee, then that perp is more dangerous to the public and warrants the massive response from LE. In most instances when a grocer or store employee is shot and killed, unless the perp as already been identified and found to be a multiple felon, there is not the need for such massive force. This may not be the way people wish it to be, but that is the way it is.
I was with you up to that point. IMHO, there is no difference between a thug who shoots a store employee for a few bucks and the one who shoots a police officer in an attempt to save his own sorry a$$. In fact the former is likely a greater danger to the public, because he killed when his own life or freedom was not perceived to be at risk.