The obvious answer is to make the public less armed than police officers.

The less obvious answer is to stop glorifying violence, including gun violence, war porn, drug kingpin lifestyles, cop/detective lifestyles, and other forms of abusive aggression in the media.

Considering that the US seems to go insane when a nipple appears on TV without a formal invitation, it's really quite strange that you can watch dramatised blood spurting out of fatal high-calibre organ wounds multiple times an hour - if you really want to.