I suspect the solution is even simpler: make the penalties for mistakenly shooting unarmed civilians significantly higher. The death of an unarmed civilian should be career-ending for the officer(s) at fault at the very least. If the penalties are higher, than that'll drive officers to prefer less-lethal weapons (tasers, pepper spray, batons) and only use actual lethal firearms after assessing that yes, the situation warrants it.

I also say this as someone with family members who have served as law enforcement officers.