As it happens, a (white) Midlands cop was just convicted of the manslaughter of a (black) man having a mental health episode. The cop tasered him twice (the first didn’t incapacitate his, the second cycle was 33 seconds long), before kicking him in the head. The cop was found with his foot on top of the man’s head when reinforcements showed up.
https://www.theguardian.com/uk-news/2021/jun/23/police-officer-guilty-of-manslaughter-of-ex-footballer-dalian-atkinson
20 odd years of incarceration will achieve nothing.
Rehabilitation, acknowledment of his guilt and educating others would be of far greater benefit
Punishment and deterrence are also purposes of the criminal justice system. I agree that in many (most?) cases those are futile. This might be one of the cases where the deterrent effect is felt: if you’re a cop that needlessly kills people, there is a chance you will be sent to prison.
Chauvin is accused of evading $450,000 of tax. Floyd was accused of having a counterfeit $50 bill before he was murdered.