Tardo Charged With Murder

From NPR:

In an affluent suburb of Boston, a community is asking tough questions following the murder of one high school student by another. The student charged in the fatal stabbing, John Odgren, suffers from Asperger syndrome, a mild form of autism.

I never really understood the argument that we shouldn't punish retarded criminals. There are two main reasons for jailing someone - the first and most important is punishment and retribution, making the criminal pay for his crime but the other reason, of nearly equal importance, is to keep violent criminals off of the street where they can commit further crimes. The fact that this kid's retarded and "doesn't even know he's done anything wrong" just seems to justify the need to lock him up, because there's clearly no remorse.