Ok so you are talking about police killing grubs/criminals/shit heads/junkies pointing guns at said police, or stabbing police, or violently attacking police whilst performing their duty, not police randomly going around executing civilians going about their daily business before heading off looking for the next victim.
What would you want police to do when a violent offender approaches them with a firearm, or points a firearm in their direction or is attempting to stab/kill/harm police??