@gryphon it depends what kind of place he's in / what he finds persuasive. my experience with ppl in that world (having grown up that way myself) is that bare stats are good to have, but they rely on a basic level of trust that is usually lacking -- the overwhelmingly common response is to find reasons to discount or rationalize the particular statistic or methodology at issue instead of engaging with the overall pattern.

from a queer intersectional perspective, imo it's hard to beat angela davis's "are prisons obsolete?" (which u can find free online) -- it's readable, not too long (50ish pages), and it is a huge infodump on the history of prisons and their rapid growth in the modern US. however... idk how that would be received? davis doesn't pull punches or soften things for white consumption, and from what u say i expect there would be considerable culture shock. that shock might be helpful in recognizing that there's a real problem or gap in his understanding, but it also might be so unfamiliar that he distrusts or rejects it after a few pages... so, i guess i'd recommend reading it yourself if u haven't, and then deciding whether to offer it to him directly or distill parts of it for your conversations while he's getting used to new perspectives.