How do you define 'Retarded'?

Warren Hill

    Hours from now, this man's fate may be a moot argument (read the latest, here), but the issue will not be soon settled.  He killed, and killed again. His 2nd victim was punished with a spike-filled board, beaten with repeated blows to the head. It was a heinous and premeditated act.
    But he was, by some observations, a borderline mentally retarded man. Therein lies the controversy. Those familiar with him believe he knows right from wrong. But the U.S. Supreme Court says anyone who is mentally retarded does not sufficiently separate right & wrong.
Is the penal system 'blowing it' and cruelly being abusive to the murderer?
    Then there's the issue of throwing a mentally retarded soul into a 'jungle rules' world of state prison? If he doesn't have the mental capacity to understand his crime, why is it okay to imprison him, yet not okay to execute him?
Is our prison a:

• way to exact punishment on people?
• way to rehabilitate criminals into nice folks?
• way to cleanse the broad society from dangerous criminals?

    So, if he's innocent of the first crime (shooting murder) due to mental 'cluelessness', is there a more humane way to protect society without putting a very vulnerable soul into a criminal jungle?  The judicial system, including the highest court in the land, has some real problems with mental health issues. Prison is being used at a huge toll in lives and treasury. Yet too many are escaping the just due for their criminal actions.
    Mental healthcare is rapidly developing very solid treatments for many mood disorders. People who have past psychotic experiences and  had no rational understanding of their dangerous acts; now have a promising future SO LONG AS THEY REMAIN IN TREATMENT. Can we mandate a life-long medical requirement, as a requisite for avoiding locking them up in either a penal  or mental institution?

• Conservatives too often react with a callous indifference, so long as undesirable people are 'put away'. 
• Liberals are too often lacking empathy with folks in the grave, and having too much sappy empathy with the abusers whom they apply wishful hopes of reform.