Many police mistakes have cost lives lately, scarcely a day goes by without an incidence of a cop (or cops) jumping to the wrong conclusion. While police need to have access to live ammunition, they can carry it with them, and load it if needed. Their guns should be loaded with tranquilizers for use when they think they have to make split second decisions. This way, suspects can be incapacitated, and any mistakes can be sorted out later.
Not only would this save lives, but police who made horrible mistakes wouldn't have to spend the rest of their lives regretting their bad decisions.