A claim of temporary insanity in a criminal court case is often related to a defense claiming that the act was a crime of passion. Crimes of passion and temporary insanity defenses are very difficult to prove. Temporary insanity can only be found by evaluating the actions in hindsight.
Witnesses are essential in a criminal court case that deals with a crime of passion. The tests that are normally used to determine insanity, such as the M'Naghten Test, the Irresistible Impulse Test, and the Durham Test, are all of limited use in such a case as well because the insanity supposedly had such a short duration.
A defense can only establish that the defendant was suffering from a bout of temporary insanity by comparing the actions the individual engaged in at the time with the actions the individual took both before and after the crime. A defense of temporary insanity was first used successfully in 1859 when a man killed his wife's lover in a fit of rage.
Temporary insanity was most likely to have been successfully invoked in a criminal court case in the middle of the 20th Century, but has become less frequently successful since then. Temporary insanity cases are invoked in less than one percent of all violent offenses. A criminal court case in which the defendant attempts to plead not guilty by virtue of temporary insanity results in a not guilty verdict less than one quarter of the time.
Temporary insanity claims have become less successful due to the tendencies of many juries to see a criminal court case when the defendant invokes the defense as an attempt to escape prosecution. Most juries consider temporary insanity claims as a method to excuse vigilante justice.
A criminal court case is likely to return a verdict of not guilty by reason of temporary insanity if two circumstances are met. The first is if the defendant has been diagnosed with a confirmed mental disorder, such as schizophrenia. If the schizophrenic is currently on medication which treats the disease, has been vigilant in maintaining compliance with an approved course of treatment, is not likely to repeat the behavior, and currently appears to be sane, it is likely that his or her claim of temporary insanity would be upheld by the jury.
A criminal court case involving a schizophrenic with a history of medical noncompliance and who appears to continue to pose a threat would likely not be found not guilty due to a bout of temporary insanity. A person with no discernible cause for the actions they undertake may also have his or her claim of temporary insanity supported by jurors.