A a retired Probation and Parole Officer I am aware that about 75 per cent of inmates have addiction as a comorbid condition to their offences. If we add to this, the number of prisoners who have a mental illness for which they are in jail now, we may come to the conclusion that the vast majority of prisoners are mentally ill. Society does not appear to have treatment. In fact it appears that jails have replaced the old "Asylums for the Insane": out of sight, out of mind.
One reason for the high recidivism (treatment failures) among prisoners is explained in:
The Forgotten Factor in the Crime Debate