See now we can track how police misconduct spreads. And officers in close proximity to officers who have records of misconduct end up being 4x more likely to use force & 5x more likely to shoot someone. We can *contact trace* police violence like a virus. https://theintercept.com/2018/08/16/chicago-police-misconduct-social-network/

Accountability systems work if they intervene & remove officers BEFORE misconduct spreads/escalates. But only 7% of excessive force complaints are upheld/result in discipline and 1% of killings result in prosecution. So these officers remain on the force. https://stories.usatodaynetwork.com/data_stories/police-use-of-force-data-a-huge-mess-across-the-u-s/

Here too, data helps us understand how to increase accountability and decrease police violence. Misconduct complaints are more likely to be upheld when depts have body cams (video=key) but much less likely to be upheld in depts with police union contracts. https://www.gothamgazette.com/city/9167-initial-report-shows-benefits-and-challenges-of-nypd-body-camera-program-for-watchdog-agency

This is because police union contracts are where the accountability system is set. Most contracts purge misconduct records, restrict misconduct investigations and help officers overturn discipline and get reinstated after being fired for misconduct. http://checkthepolice.org 

In fact, police depts with union contracts that grant more procedural protections to officers accused of misconduct are:
1) more likely to be reported for misconduct
2) less likely to uphold misconduct complaints
3) more likely to kill unarmed people https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3246419

So the contracts matter, and they need to be re-negotiated to increase levels of accountability and to reduce police violence. But what about the exceedingly low rate of officers being prosecuted? Well, we know more about this topic now than we did 5 years ago. For example...

While only 1% of all killings by police result in officers being charged with a crime, this 1% isn’t evenly distributed. There are a handful of places that routinely charge officers while almost every other place fails to do so. And those places tend to have Black prosecutors. https://twitter.com/samswey/status/690599927588585473

We still don’t know what tactics these prosecutors are using to secure indictments in these cases, but electing prosecutors (esp. Black prosecutors) who genuinely care about holding police accountable is important. This + video evidence are factors that can make the difference.

So we now know:
1) which depts have the worst police violence rates & which are reducing it
2) a set of interventions/factors associated with reducing this violence and increasing accountability

By continuing to study & scale up what works we can end police violence nationwide.