The current legal system was created by the Parliament of Canada after the previous system was ruled unconstitutional by the Supreme Court of Canada in R. v. Swain. The new provisions also replaced the old senseless defence with the current mental disorder defence.  There is generally a presumption that criminal accused are mentally sound, just as there is a presumption of innocence. Therefore, at least one defendant who pleads mental illness must provide evidence that rebuttals this presumption. Some states require prosecutors to prove mental health beyond a reasonable doubt or a preponderance of evidence (Elkins, JR, & Students, 2010). Both important (mental illness) and minor (loss of reason) criteria are legal folly. In 1984, Congress passed the Comprehensive Crime Control Act and President Ronald Reagan signed it into law.
The federal defense for mental illness now requires the defendant to prove by “clear and convincing evidence” that “at the time of committing the acts constituting the offense, the defendant was unable to discern the nature and quality or illegality of his acts by reason of serious mental illness or mental impairment” (18 U.S.C. § 17). This is generally seen as a return to the norm of “distinguishing right from wrong.” The Act also included the Defense Against Insanity Reform Act of 1984, 18 U.S.C. § 4241, which provides sanctions and other provisions for treating offenders who suffer or have suffered from a mental illness or disability. A recent example of this gap is the case of Andrea Yates. She had a long history of depression and postpartum psychosis. She was undeniably psychotic when she drowned her children. Yet she was convicted at her first trial for telling the 911 operator that she had done something “wrong” and later confessed that she had waited for her husband to go to work. She also locked up the family dog so she wouldn`t be deterred from killing the children. The jury concluded that she still knew right from wrong and was therefore not legally insane, although they agreed she was psychotic at the time. Finally, paragraph 2 of section 4.01 of the Code is of particular importance. There, the use of the defense of insanity for psychopaths and sociopaths is expressly prohibited.
The introduction of a guilty but mentally ill option in 20 states recognizes mental illness and the need for treatment, but does not exclude punishment. It would apply in cases where mental illness is seen as alleviating guilt, but not as extinction. The legal consequences are that the convict is sent to prison and treated there – not to a psychiatric institution. The defendant will complete his sentence even if he is cured, while an accused found not guilty of mental illness will be released after recovery. Television shows and films depict defendants who have not been convicted on “mental illness.” In real life, criminal defendants are not as successful with a senseless defense or “crazy plea,” as the popular media shows. The concept of responsibility is related to our most fundamental beliefs about human nature and dignity and the daily experience of guilt and innocence, guilt and punishment.  Punishing a person who is not responsible for the crime is a violation of fundamental human rights and fundamental rights of the Indian Constitution. It also leads to due process if that person is unable to defend himself or herself in court and invokes the principle of natural justice.  The affirmative defence of legal insanity applies to this basic principle by apologizing to mentally disturbed offenders whose disorder deprived them of a rational understanding of their behaviour at the time of the crime.  Therefore, it is generally accepted that the inability to commit crimes exempts individuals from punishment. This is recognized by the legislation of most civilized nations. [1,3] Even in India, Section 84 of the Indian Penal Code (IPC) deals with “the act of an insane person” and deals with defence against mental illness.
 In the recent past, however, some U.S. states (such as Montana, Idaho, Kansas, and Utah) have banned defense against insanity.  This issue has sparked serious debate among medical professionals, psychology and lawyers around the world.  Non compos mentis (Latin) is a legal term meaning “no common sense”.  Non compos mentis is derived from the Latin not for “not”, compos for “to have commandment” or “to put together” and mentis (genitive singular of mens), meaning “of the spirit”. This is the direct opposite of compos mentis (a healthy mind). In the United States, a criminal defendant can plead mental illness in federal and state courts in any state except Idaho, Kansas, Montana and Utah.   However, defendants in states that do not allow the mental illness defence can still prove that a defendant was incapable of forming the intent to commit a crime because of mental illness.
 Although controversial, most states and the federal government recognize a senseless defense (18 U.S.C., 2010). Montana, Utah, Kansas, and Idaho are the only states that do not (Findlaw.com, 2010). The defence of mental illness is the subject of much debate because it excuses even the most vicious and heinous behaviour, and in many jurisdictions, legal insanity functions as the perfect defence leading to acquittal. However, the crazy defense is rarely used and hardly succeeds. This is usually due to the difficulty of proving legal insanity. Your defense will rely on evidence proving that you – the accused – were “insane” when the alleged crime occurred. A successful defence against mental illness means that you are not criminally responsible for breaking the law. In Kahler v. Kansas (2020), the U.S. Supreme Court ruled in a 6-3 decision that a state does not violate due process by abolishing a senseless defense based on a defendant`s inability to distinguish right from wrong.
The Court noted that state governments have broad discretion to choose laws that define “the exact relationship between criminal culpability and mental illness.”  The second component of § 4.01 includes volition-based analysis.