M'Naghten Rule was the legal rule established.
Step-by-step explanation:
The M'Naghten Rule suggests the legal rule of deeming the defendant innocent of a crime if it is proven that during the act of the crime the individual didn't know the nature of his/her actions. This is also possible if she didn't know it was wrong.
The rule suggests testing whether the accused was sane at the time of wrongdoing. If the person was sane then he will be charged with the legal procedures. But if not, the accused is spared. Basically, the rule is a test of the criminal's sanity.