Young Black males.
In any population segment, the criminal class is going to be a relatively small subset. It HAS TO BE a small sub-segment, for the same reason that predators must be relatively few compared to the number of prey -- because otherwise you run out of prey
Somebody who is supporting himself thru robbery must commit a LOT of robberies per week. What's the average take per robbery? How much money, on average, does anybody here have on him when walking the street?
I would figure the average mugging would net $50, and the average convenience store holdup maybe $200. That's not enough to support a drug habit and get female companionship unless the guy is doing at least one or two robberies per day. If a career criminal is permanently removed from the environment, that's a reduction of hundreds of crimes per year.
The judges can refuse to incarcerate or execute a criminal, but it's real hard for a judge to FORCE a police department to arrest a homeowner for shooting a criminal, if the police and prosecutors just decide to not persue such cases