How to solve this systemically, so it couldn't repeat? I guess we'd need details.

This Twitter thread [1] points to research on the subject of reducing police violence, which I found fairly informative.

[1] https://twitter.com/samswey/status/1180655701271732224?s=19

See also this recent post which many people clearly found relevant, but which a small minority managed to censor by flagging: https://news.ycombinator.com/item?id=23373185