Do these percentages reflect previous problems with the law? Prior records, etc?
Possibly. There are a bunch of factors which might be in play. Anything from appearance to attitude to perhaps even family supervision.
I know for a fact that appearance matters. My brother was arrested with a bunch of other (all white) kids. All were equally involved in committing the crime. The other kids got crew cuts and nice new suits before seeing the Judge. My brother, refusing to be something he was not, (and my parents, sensing that the kid needed a wake up call) didn't cut his hair, wore regular (decent and clean) clothes. He was the ONLY one to receive jail time.