I have dealt with a lot of criminals professionally, but comparatively quite few who have done long prison sentences. Those who did tended to fall into one of two patterns, the divergence between which I find a little disturbing.
Those who committed the worst, most violent crimes tended either to "find religion" and rehabilitate into a very different person, or else to withdraw into themselves, and upon release be hardly seen or heard from again until they quietly died, and it made the news and shocked their neighborhood.
On the other hand, those who committed comparatively "minor", sometimes non-violent offenses and yet received and served long prison sentences, usually under inflexible federal sentencing guidelines, did NOT rehabilitate, and instead tended to BECOME very violent and dysfunctional. Sometimes they were an otherwise fairly ordinary person who for whatever reason committed tax fraud, insider trading, racketeering, corruption, or whatever. When they emerged from prison they were MORE anti-social and, to my view, MORE dangerous to society than before. Some believed they had been abused by an imperfect system, and in some cases it was time for payback.
Our criminal justice system of punishment is based on some very eccentric and often questionable assumptions, and to a great extent is the contorted product of historical accident and political machination.