As a forensic psychiatrist writing crime novels, I'm often asked about criminal cases involving the insanity defense (Not Guilty by Reason of Insanity, or NGRI). These are usually controversial and the most infamous ones are covered extensively by the media -- John Hinckley; the Unabomber; and more recently, James Holmes, the Aurora, Colo., killer.
In reality, NGRI pleas are quite rare, involving less than one percent of criminal cases; and fewer than one quarter are successful.
At the heart of the NGRI defense is the claim the defendant either lacked the capacity to know right from wrong (was brain-damaged, intellectually impaired) or had a mental disorder when the crime was committed, causing an inability to act within the law's requirements. An example would be a paranoid man who fervently believes the FBI and CIA are following him, and because of this delusion, shoots someone walking behind him on the street.
When I was a psychiatric resident in a large hospital, the police brought in a man who was ranting wildly. He had stabbed his six-year-old daughter ten times in the heart. The prisoner, a paranoid schizophrenic, claimed he heard the devil's voice commanding him to do it. He believed his daughter was a child of Satan. Months later, I was asked by the defense to re-examine the patient, this time at a state facility. He was as psychotic as ever and steadfastly clung to the belief he had done the right thing by returning his daughter to the devil. At trial, he was found NGRI and remanded to a state hospital where he remains, nearly 30 years later.
Occasionally, we hear of a defendant claiming "temporary insanity" after committing what is commonly known as a crime of passion. The defense posits a temporary loss of ability to discern right from wrong because of an extreme mental state brought on by an unanticipated, shocking situation, the classic example being a man coming home to find his wife in bed with his best friend. Juries, for the most part, are unsympathetic to such claims, rejecting them because they expect adults to exercise more self-control, even in extremely trying situations that engender rage.
Because NGRI defenses are very difficult to prove, they rarely are brought by defendants. At trial, forensic psychiatrists testify about the defendant's presumed mental state at the time the crime was committed. The jury must make its decision based on that testimony. The current functioning, appearance and demeanor of the defendant is of no bearing. It is the competing expert testimony presented by the forensic psychiatrists, which must be evaluated by the jury, and form the basis for its determination.
The biggest misconception about NGRI pleas is the popular belief that, if found Not Guilty by Reason of Insanity, the defendant leaves court a free person. The thinking is, the defendant got away with it.
This is not true.
If a jury concludes a defendant is Not Guilty by Reason of Insanity, he or she is remanded to a state hospital for an indefinite period of time. That confinement is for treatment of the mental condition that allowed the crime to occur. The hospitalization is usually very long, and may exceed the time which would have been served in prison had the defendant been found guilty. The average stay in a locked mental hospital for an insanity acquittee is 42.6 years in Connecticut, Office of Legislative Research whereas the prison term for the same crime is about 7.5-10 years National Judicial Reporting Program.
In most states, psychiatric facilities for NGRI acquitees are under the aegis of the Department of Corrections. A review board meets annually to decide if the acquittee has been "restored to sanity." In most cases, "restoration of sanity" rarely occurs.
So, a successful NGRI plea doesn't mean the defendant got away with a single thing. In fact, it's often a life sentence.
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