This is something that has been much on our minds of late. Read Mental Illness And Crime: What The Legacy Of Dorothea Dix Hath Wrought. Excerpt:
In the 1830s, jails were an all-purpose solution for a lot of issues. Inmates lived in squalor and people truly did not want to be there so there was a lot less crime. The downside was that nobody really cared about the people who did not belong there, like those with ‘retardation’ who had been abandoned, or people who were mentally ill but not criminals.
Dorothea Dix was the activist whose efforts led to the first generation of American mental asylums. At the age of 39, she happened to visit a local jail to do a Sunday school sermon for female inmates. She found that 
criminals, retarded people and the mentally ill all lived together in terrible, unheated conditions. When she asked why, she was told “the insane do not feel heat or cold”(Viney&Zorich, 1982). Not exactly evidence-based.
No, but here is something that is evidence-based: All of the high-profile multiple murders committed in this country in recent years have a common thread, that being under-treated or untreated mental illness. Adam Lanza should have been in an asylum; ditto for James Holmes. (Islamist murderers fall into another category and belong not in asylums, but in graves.)
Too many people are walking around that shouldn’t be. (Much of Congress and the Executive Branch may well belong in asylums, but that’s a discussion for another day.) Upon a time these people would have been locked up – perhaps cruelly and in lousy conditions, but locked up.
Surely we can do better now?
Why do we not have a new breed of mental institution, where the conditions are humane, where the treatable can be treated and the untreatable maintained away from peaceable society?
The Science 2.0 article linked here concludes:
We have so many more mental patients in jails not because we have returned to the America of the 1830s, where the mentally ill are just thrown in jail so we don’t have to think about them, but because mental illness has been turned into a scientifically subjective loophole and therefore part of a cultural agenda.
The author is missing a cogent point. We have more mental patients in jail because we do not attempt to remove potentially harmful people from society until they have already committed a crime. Adam Lanza was known to be potentially dangerous. So was James Holmes. Why were they running around loose?
I make my living in large part by teaching high-tech companies how to do root cause analysis. One of the ways you find a root cause is to look for commonalities in the circumstances of repeated events. As noted, the common thread in the high-profile multiple murders we have seen lately is untreated or undertreated mental illness.
Until we address that, nothing else we as a society do will prevent another Adam Lanza or James Holmes from running amok.
