Time passes. Twenty years from now Jared Loughner, sentenced to life in prison, could be classified as sane by diverse experts in mental illness. Essentially that's the situation with John Hinckley, who had shot the late president Ronald Reagan. His lawyers are requesting extended stays for him outside the mental hospital.
Can mental illness "burn out?" Also, there is the phenomenon called "neuroplasticity." The brain can be reconditioned and new pathways generated. That could explain how the aging such as as Clint Eastwood could do very different work than they had in earlier years. Could a relationship, religion, or reading change the brain of nuts?
Society doesn't like to consider this issue. It is wary of master cons faking sanity and conventional moral values. Few are ready to let Son of Sam out of the joint.
In my own family, the European European side (my mother's maiden name was "Miksza") is filled with madness, addiction, and creative forms of self-destruction. Those who did manage to live long enough did show a return to sanity. The usual onset of insanity was late adolescence. That's why the issue interests me. No former pinnacle of mental health myself, I have been amazingly stable since 2003 (Download Geezerguts). The trouble had begun when I was in graduate school.