If I was the cops, I would start a skunk works style database of recurring offenders, arrests, judicial decisions and outcomes.

Once you have a good number of smoking-gun cases of repeat violent offenders due to DA inaction, then leak it to the media. Name and shame the DA, make sure the voters / people in power know where the weak link is and give them a better alternative.

Cops get apathetic because their arrests have no effect, but the paperwork can be useful to solve the fundamental problem.