The Insanity Defense, and why it's seldom used

We’ve seen it used a million times on TV, but in the real world successfully asserting an insanity defense[1]is rare and difficult.[2]
 
When the court looks to whether a person in “insane” for the purposes of a criminal matter, it uses what we call the M’Naghten rule.  In order to be insane, the defendant must no—at the time of the offense—have been able to either understand the nature and quality of his or her act or must not have been able to distinguish between right and wrong.[3]  For example, a person could be held to be insane, and would have a defense to animal abuse charges, if they heard imaginary voices, telling them that the world was going to end shortly unless the defendant sacrifices a goat to the God Anived, so the defendant does, indeed sacrifice the goat. However, if a defendant who suffers from depression or anxiety, and only felt relief when she was hitting her boyfriend would not be able to successfully use the defense, even though the anxiety or depression caused her not to care about the possible consequences of hurting the young man. 
 
Because insanity is a legal defense, it is the defendant, not the government, that bears the burden of proving by a preponderance of the evidence[4]this aspect of a case. At trial, the two issues (first, whether the defendant did the act for which they are being accused, and then second, if they were insane when they committee the act) are heard separately.[5]The issue of guilt is heard first, with this portion of the case being just like what you see on TV: the various witnesses to the crime testify about the evidence. Then, if the jury finds the defendant guilty, the jury decides the issue of sanity. During this portion of the case, usually the only witnesses are qualified medical professionals. 
 
However, a lot of people do not realize that a defendant whois held to be insanedoes not get a free pass; they are ordered to be committed to a state hospital for treatment, not only to try to rehabilitate the defendant, but also to protect society.[6]A defendant can be held in that mental facility until one of three things happen: (1) doctors believe that the defendant has regained sanity, (2) the maximum term of imprisonment for that crime has expired[7], or (3) the doctors feel that the defendant would be successfully in addressing the underlying issue via outpatient treatment program. 
 _______________
 
[1]Found in Penal Code § 25

[2]Recent statistics claim that only 1% of all defendants assert the defense. 

[3]In the 90s, the legislature amended the law to prevent the court from finding a criminal defendant insane based solely on the basis of  a seizure disorder, a personality or adjustment disorder, or addiction to/abuse of an intoxicating substance.

[4]More likely than not. 

[5]Of course, a defendant can enter a plea of “guilty by reason of insanity,” in which they admit they did the bad thing they are accused of, but claim the defendant should not be held accountable due to the defense of insanity. 

[6]People v. Superior Court (Williams) (1991) 233 Cal.App.3d 477, 485.

[7]That said, a defendant may be further confined, if the person still has a diagnosed mental disease or disorder and is a substantial danger of physical harm to others.