Raised in <1% of all criminal cases; successful in only 25% of those
Under the M’Naghten Rule, the burden of proof is on the defendant
An offender is insane under this test if mental illness prevents the offender from knowing the difference between right and wrong
This renders the defendant "not guilty" and exempts them from punishment
Competency to be Executed
According to ABA Standard 7-5.6:
Convicts who have been sentenced to death should not be executed if they are currently mentally incompetent. If it is determined that a condemned convict is currently mentally incompetent, execution should be stayed.
A convict is incompetent to be executed if, as a result of mental illness or mental retardation, the convict cannot understand the nature of the pending proceedings, what he or she was tried for, the reason for the punishment, or the nature of the punishment