HN has always seemed to me to be a community that is moved by data-driven approaches, and this topic has a pretty clear motivation to reduce police violence. As a result, I think some people may be interested in reading up on Comapign Zero's[1] 8Can'tWait initiative (
https://8cantwait.org/), which has identified, tracked [2], and advocated for 8 policy implementations across municipalities in the U.S. which meaningfully reduce instances of police violence.
The policies include a Use of Force Continuum, Comprehensive Reporting requirements, De-escalation Requirements (which, here, in the context of mental health response is particularly valuable), and more. There are links at the bottom of their website which can help you dig more into their methods, if you're interested.
[1] https://www.joincampaignzero.org/
[2] https://useofforceproject.org/#review