What is the insanity defense?

Published 1:25 pm Thursday, February 28, 2019

By Holly Westbrook


What is the insanity defense? The Cornell Law School website states, “the insanity defense refers to a defense that a defendant can plead in a criminal trial. The defendant admits the action but asserts a lack of capability based on mental illness.” 

The federal insanity defense requires the defendant to prove, by “clear and convincing evidence,” that “at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts.” 

An important factor to the insanity defense involves the establishment of legal competency, otherwise known as competence to stand trial. In accordance with due process requirements, a criminal defendant cannot stand trial if he or she is deemed legally incompetent.  

Texas has a strong history of not accepting the insanity defense as a plea of “not guilty” within case files of the judicial court archives.

The Texas legal proceedings can be found in the Code of Criminal Procedure, Title 1. Code of Criminal Procedure, Chapter 46C. Insanity Defense, Subchapter A General Provisions.  

In 1843, Englishman Daniel M’Naghten shot and killed the secretary of the British Prime Minister, believing the Prime Minister himself was conspiring against him personally. The court acquitted M’Naghten “by reason of insanity,” and sentenced him for life in a mental institution. Even with Queen Victoria ordering the court to develop a stricter insanity test, this became the first famous legal one for the insanity plea.  

In a criminal case, a defense by the accused that he or she was briefly insane at the time the crime was committed and therefore was incapable of knowing the nature of the alleged criminal act, is temporary insanity, Nolo’s Plain-English Law Dictionary said.  

The M’Naghten rule became the standard for insanity in the United States and the United Kingdom and is still the standard for insanity in almost half of the states. 

You can visit www.texas.gov for more information.