I think if mental people commit murder, rape, or anything that can hurt others should be arrested, they may not know what is going on, but if they get let loose they could kill others again. I think that they should be arrested even if they robbed some place, just not as long as others.
Should we not, at the very least, institutionalize people with mental illnesses that commit serious crimes such as rape or murder? Say we let people like James Holmes or Jared Lee Loughner loose. How could someone logically think that's a good idea? We need to get these people the help they need BEFORE they commit crimes.
If a two year old wouldn't be charged with assault and battery, neither should an adult with a damaged brain. These kinds of people don't realize the damage they are doing, they don't realize who they are hurting, and a lot of them don't have a theory of mind, which would mean that they know that others are self aware. I think they should be put in a mental hospital, but to throw them in prison and ruin their lives for something that they didn't understand is a horrible thing to do.