This defense is probably the most used and abused line of defense we have. Who is to say if the defendant was insane at the time of the crime? The victim, witness, or the testimony of "expert" witness? People who plea insanity to get out of their own actions should be punished just as bad as the crime they committed or even worse in some cases. Who is to say the person is insane or not though so when they plea the "Insanity Defense" they could be insane or they could be trying to get out of murder or just a robbery so you have to trust your instinct I think a give them the correct punishment. The insanity defense refers to the concept of the mental state of the person who committed the crime. In the end the terms of such a defense are to be found in the instructions presented by the trial judge to the jury at the close of a case. The jury will have to take all the evidence presented by the lawyers" "expert" witness to decide if the defendant is truly mentally ill. Legal researchers believe that the insanity defense and mental illness are not synonymous. Insanity includes not only mental illness but also mental deficiencies. This definition of insanity leads to many problems of how to determine the difference between legalistic criminology and scientific criminology.
In order to determine the mental state of the defendant lawyers use tests. At the center of the legal use of insanity lies the mens rea, the non-physical cause of behavior In order to analyze the mens rea lawyers apply several rules used by psychologists. These rules include the Irresistible Impulse test and the M"Naghten Rule. The M"Naghten rule reads: A defendant may be excused from criminal responsibility if at the time of the commission of the act the party accused was laboring under such a defect of reason, from a disease of the mind, as not to know the nature and the quality of the act he was doing, or if he did know it, that he did not know that he was doing what was wrong.