Disclaimer:

I assume, in this, a few things. These are:

1) A healthy person will seek things that benefit them and if they benefit the group, so much the better.

This key assumption underlies all existing understanding of cooperation, competition and conflict. It's very bad news if it's wrong, so we make it axiomatic and define all who don't nest it as unhealthy. It's a necessary fudge because true altruism is too rare to examine and define, whereas greed is the most common practice that is unhealthy to the group

1. The brain is the seat of all decisions, and the body and microbiome tune it chemically. There is nothing external that matters here.

(Note to theists: There may be external factors, in whatever sense you like to believe. If you wish to believe in possession, I won't say you're wrong but I will say that this proposal has nothing to say about it.)

1. Criminals are therefore unhealthy but may be unhealthy for a number of reasons. However, this simplification ignores all of that. It all comes out in the wash.

Here, then, is the method.

Step 1: Neurological rehabilitation.

a) The criminal is subject to very high-res MRI and fMRI scans, plus DNA check.

The DNA check is mostly for the warrior gene, for identified medical responses, abnormal methylation and other tell-tale signs of something going wrong deep down in the biological level. The scans should help, as hyperactive or hypoactive regions might indicate problems. Behaviour-altering tumours and concussion damage can arise at any age, as well.

This level tries to bring the brain's biochemistry under control, so that the brain gets to make real choices.

In a fair number of cases, the issue won't be at this level. They'll be certified QAed and handed up a level.

Step 2: Personal therapy.

Therapy has an extremely low success rate, but I think that's because it's trying to build on broken foundations. Step 1 fixed those, so Step 2 should have a better chance of removing undesirable behaviours and turning the unremoveable ones into something more productive.

Step 3: Job Therapy

Find what work the person actually enjoys, turn it into something that pays, have the person carry out productive, meaningful work at full wages (that can't be spent yet), where the product is sold outside the prison and where the prisoner, work and "company" can continue afterwards if it turns out the person simply needs to live in a quasi-hermitage. So a prisoner can elect to extend their term as a half-way inpatient/outpatient arrangement.

Note: Maths, art, poetry, composing symphonies - these are all valid work, provided that the results are publishable, receive sponsorship or recognition, or can sell. It doesn't have to be physical, it just has to fix your reputation and give you financial support.

Those who exhibit criminal modes of thought go through the cycle again, on the assumption that something was missed.

At all points, a prisoner is treated as a person. Their conditions would follow the Norway model, as would recreation time. During treatment, they're a person where, for want of a better phrase, a silicon chip inside their head has switched to overload. Finding it and fixing it doesn't mean the person's lesser, it just means there was a cheap part. The fish might've been on weight watchers and had the wrong fats for what was needed. Who know, who cares, as long as it's fixed enough to have a decent life?

What about unintentional criminals who fell on their faces in life and survived through theft? They may well have PTSD, which this structure can lessen or fix. Same with any mental scars from their conduct. First the neurology is fixed, then the psychology, followed by removing instability and replacing it with a stable, non-exploitive career.

On leaving, the probation officer is informed of the person's direction in life, assets earned and concerns noted.

This idea probably needs fixing some, but the basis (foundations, structure, career) seems to be sound.

We need to stop thinking punishment versus rehabilitation and start thinking rehabilatation. Punishing offenders of the law ultimately is a short term fix and does nothing to help in the long run. The only answer is rehabilitation when possible, it is the only viable long term solution

The problems are too numerous. Define crime as mental illness from first principles and you must defend why people who are not engaging in criminal activity but have a measurable mental illness should not be incarcerated by default. There are elements of pseudoscience here, such as the warrior gene reference. The idea here is very goodhearted, but it amounts to a system where people have their rights revoked by medical boards. What do you do with the patient-prisoner who refuses to be cured? Since the illness is, in some sense, voluntary behaviors, the possibility of a patient-prisoner who chooses to continue to be "ill" approaches 1. Are they incarcerated forever?

There is also the danger, in combing health and criminality, in the creation of moral crimes. If the doctors agree that homosexuality is psychologically deviant, they can agree that it is a crime and can do the same for any non-standard behavior or belief.

Criminal behavior stems from a form of mental illness, or from a feeling of necessity.

Either they feel compelled to perform anti-social behavior, or they feel their status is such that they have more to gain from engaging in criminal behavior than from behaving in a legal manner.

The behavior toward both, however, is the same: treatment and correction.

In the case of the former, mental health treatment is required. If the person is dangerous, they should be incarcerated, otherwise home treatment should be the order of business.

In the case of the latter, there must be underlying reasons that make the person believe that criminal behavior is preferable to legal behavior. These underlying reasons must be removed or the situation will not correct itself.

Most sufferers of most mental illnesses have a lower incidence of crime than the general population. There are only a handful of disorders where the reverse is true and in the vast majority of those disorders, the patients are psychotic. Even in those cases, proper treatment prevents the patients from engaging in illness-related crimes.