Though popular fodder for the media because they are profitable, killings by cops are extremely rare. I believe there are about 1000 murders-by-cop in the U.S. (a nation of 330,000,000 people) in a year, and in the vast, vast majority it is not at all ambiguous whether or not the cops acted in good faith. Picture someone running around stabbing people: the cops killing that person isn't something most people would find questionable.