Criminal insanity is a defense which may be used in a criminal case. The criminal insanity defense argues that someone should not be held responsible for a crime because she or he did not understand the ramifications of the crime at the time due to an altered mental state. When someone is found not guilty by reason of insanity, it means that at the time the crime was committed, the person's mental state was such that he or she could not act willfully. The standards which must be met in order for this defense to be accepted vary around the world.
The idea behind criminal insanity is that most legal systems believe that it is unethical to hold someone responsible for a crime if he or she does not understand the crime. People sometimes confuse criminal insanity with mental illness, because of the use of “insane” to describe people who are mentally ill. In fact, mentally ill individuals can be and are held responsible for committing crimes, and not all people who are found criminally insane are necessarily mentally ill.
Criminal insanity is also not the same as competency to stand trial. When someone uses an insanity defense, it is used to argue that the person is not guilty because of his or her state of mind at the time of the crime. When an individual is found incompetent to stand trial, it means that the person lacks the mental capacity to understand the proceedings and cooperate with a lawyer. Just as people are not held responsible for crimes they commit without being aware of it, people are not required to stand trial if they cannot understand what is happening. If the accused becomes competent later, the case can be tried.
For a classical ruling of “cognitive insanity,” it must be shown that the person did not understand the difference between right and wrong at the time of the crime. In some regions, a defense on the grounds of volitional insanity or “irresistible impulse” is allowed. In these cases, someone understood the difference between right and wrong but was unable to act upon it. Mental illness is sometimes invoked in this type of defense, because the defense may argue that the defendant's mental illness restricted impulse control.
If someone is found not guilty by reason of insanity, the court usually strongly recommends psychiatric treatment, and may require it in some cases. This treatment is not intended to be penal in nature. It is also important to note that since this defense is sometimes exploited, courts are very particular about insanity defenses to avoid situations in which people who should be held culpable avoid punishment because they are able to convince the court that they were not of sound mind at the time of the crime.