Each false conviction, plea bargain or guilty plea should count as -20 convictions.
It all comes down to incentives. Murdering this man was probably great for all of the involved people’s careers (and I’d be surprised if he is their only victim). If it was a potential career-ender, they’d find some other way to game the system, or others would be promoted instead of them.
The same story plays out millions of times a year in the US (though usually with lesser crimes); it’s clearly a systemic issue.