In Arizona you have to be mentally competent to stand trial - meaning you have to understand the charges against you, bascially understand the court process and be able to assist your attorney.

If a person is found to be not competent to stand trial, but can be treated to be restored to competency, they are placed into a treatment program for a period of time. Once they are determined by the doctors to be competent then they are tried.

If a person is insane, they may be ordered into treatment and hospitalized. If a person claims to be insane at the time they committed the crime, they usually will stand trial, and can be found 'guilty but insane' and they will be sentenced to the State Mental Hospital.

It is very hard to fake mental illness or unstability and get away with it - as usually at least 2 doctors evaluate the person seperately, and sometimes additional doctors do evaluations if the first 2 don't agree.