What Does the Legal Term “Not Guilty by Reason of Insanity” Mean in California?

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When a defendant and/or the defendant’s criminal defense attorney uses this term to avoid prison time for having committed a criminal act, it is upon the defense attorney to prove this to the court. In most other cases, the prosecutor must show how a defendant is guilty of a crime, while the defense attorney defends against what the prosecutor presents to the court.

What is California’s The McNaghten Rule?

Several states in the U.S. still use a plea of insanity but how that is achieved is determined by different means in those states. California uses the McNaghten Rule (spelled several different ways) which was first applied in 1843 during the case of Daniel M’Naghten who had tried to assassinate the Prime Minister of England but hit his secretary instead.

Five questions were posed to the common law court judges of that time and two questions became the basis for how a defendant could be considered insane at the time a crime was committed. Both questions remain today as the defining insanity parameter in the California court system.

If you are absolved of the crime, you are set free and will not go through a second trial to determine your insanity

The first question addresses whether a defendant had such a defect of reason from disease of the mind, that the defendant did not know the nature or quality of the crime he/she was committing. The second question concerned whether if the defendant knew that what he/she was doing was wrong.

This is known as the “right and wrong” standard and was first applied in California in 1864 in the case of the People v. Coffman. Read more about The McNaghten Rule here. This rule, however, cannot be used when the defendant was using drugs or alcohol at the time when the defendant committed the criminal act.

Pleading “Not Guilty by Reason of Insanity” – Two Ways

The California legal system allows you to use the McNaghten Rule in two ways. Your criminal defense attorney, who knows your case well and how likely you will be absolved of the crime, will advise you of which way to make your plea.

  • Dual plea of “not guilty” and “not guilty by reason of insanity” – Bifurcated Trial

When you make the dual plea, you will first go through a regular court trial that concerns only whether you were guilty of the crime or not. If you are absolved of the crime, you are set free and will not go through a second trial to determine your insanity.

If you are found guilty, then you undergo a second trial that determines whether you were insane when you committed the crime. You must show the evidence of this, including expert testimony from medical professionals who have examined and tested you. The two issues are that you did not understand the nature of your act and you did not understand that what you did, was wrong.

  • One-step plea of “not guilty by reason of insanity”

You know you committed the offense but claim you were insane at the time you committed the act.  You would only receive a “sanity trial” on whether you were insane when you committed the act or not. If you are declared insane when you did the act, then you will be committed to a state mental hospital. If not, you will be sentenced as guilty of the crime you committed, likely leading to jail time.

Call us at once if you need help with your insanity plea case. 619-234-2300

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Kerry L. Armstrong


Attorney Kerry Armstrong opened up his law firm in June 2007. Mr. Armstrong attended Thomas Jefferson School of Law, San Diego, California, and received his B.S. from Middle Tennessee State University. Kerry L. Armstrong became certified by the State Bar of California’s Board of Legal Specialization for criminal law in August 2020, making him one of the few criminal defense attorneys with a criminal law legal specialization certificate in San Diego County.  Between 2014 – 2019, Mr. Armstrong was selected for inclusion in the California Super Lawyers list, an honor only awarded to 5% of the nation’s attorneys.

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