When a court suspects that a criminal was legally insane at the time he or she committed the crime for which he or she stands trial, it may not hold the person accountable by reason of insanity. For an insanity defense to apply in New York, the defendant must prove that he or she did not comprehend what he or she was doing; that he or she acted on an irrepressible impulse; or that he or she failed to distinguish right from wrong at the time of the crime. To ensure that defendants do not abuse the insanity defense, the courts have implemented a four-part test. 

According to FindLaw, the insanity test was first used in the late 16 century, when the courts ruled that if a madman or a lunatic kills someone at the time of his lunacy, the courts cannot hold him accountable. In the 18 century, the courts established a “wild beast” test, which serves as the basis for today’s insanity defense test.

Depending on in which jurisdiction a case is heard, the courts use a combination of tests. The four tests the courts use are as follows: 

  •       The “Irresistible Impulse” Test: This test assumes that the defendant was powerless to control his or her impulses at the time of the crime because of mental disease.
  •       The “Model Penal Code” Test: The test seeks to prove that a defendant either did not understand the criminal nature of his or her actions or was unable to act within the limitations of the law because of his or her diagnosed mental defect.
  •       The “M’Naghten Rule”: This test seeks to show that the defendant did not know right from wrong at the time of the crime because of his or her “disease of mind.”
  •       The “Durham Rule”: This test seeks to prove that, regardless of the existence of a mental defect diagnose, the defendant’s mental state resulted in the criminal act. 

According to the American Bar’s Criminal Justice Standards on Mental Health, Standard 7-3.3, a person has a right to defend him or herself against criminal charges via a defense-initiated evaluation of the defendant’s mental condition. If the defendant cannot afford an evaluation, the jurisdiction is liable to make funds available to pay for an evaluation by a qualified mental health professional, or the professional of the defendant’s choice.