California’s “Insanity Defense” – The McNaghten Rule

Under California’s insanity defense, you cannot be convicted of a crime if you were legally insane when you committed it.¹ You are considered legally insane if you either:

1. Did not understand the nature of your criminal act, OR
2. Did not understand that what you were doing was morally wrong.²

This definition of legal insanity is known as the “McNaghten (sometimes spelled M’Naghten or McNaughten) rule.”³

If you plead “not guilty by reason of insanity,” you will then need to prove at trial that:

• it is more likely than not that you were legally insane when you committed your crime.⁴

Then if the jury finds you “not guilty by reason of insanity,” you will be:

• committed to a state mental hospital instead of being sent to prison.⁵

Examples

• A delusional woman steals her neighbor’s vacuum that she believed belonged to her. Since she did not understand she was taking someone’s property, the insanity defense may work for her.
• A schizophrenic man grabs a boy from the park and takes him to ice cream because he believes God told him to. When the man is later charged with kidnapping, he can claim insanity because he did not understand that what he was doing was morally wrong.

In order to help you better understand the insanity defense, our California criminal defense attorneys⁶ will discuss the following:

• 1. What is the legal definition of insanity in California (the McNaghten Test)?
  • 1.1. The McNaghten rule in California
  • 1.2. The insanity defense and drug addiction
• 2. How do I prove insanity as a legal defense in California?
  • 2.1. “Preponderance of the evidence” standard for the insanity defense
• 3. How do I enter a “not guilty by reason of insanity” plea in California?
  • 3.1. Entering a “dual” plea of “not guilty” and “not guilty by reason of insanity”
  • 3.2. Sanity hearings in California
  • 3.3. Entering a single plea of “not guilty by reason of insanity”
• 4. How does an insanity plea affect sentencing?
• Additional resources

If, after reading this article, you would like more information, we invite you to contact us at Shouse Law Group.

1. What is the legal definition of insanity (the McNaghten Test)?

Under California law, a person is “legally insane” and able to assert the legal defense of insanity if, because of a mental illness, s/he EITHER

1. Cannot understand the nature of his/her criminal act, OR
2. Cannot distinguish between right and wrong.⁷

This legal definition of insanity is known as the McNaghten (sometimes spelled M’Naghten or McNaughten) rule.⁸ This interesting name comes from a 19th-century British defendant who is the basis for the following example:

Example: Daniel McNaghten suffers from paranoid delusions. He believes the government is out to get him. So in 1843 Daniel attempts to assassinate the Prime Minister of Britain and ends up shooting a government secretary instead.

Daniel is tried for attempted murder. But he is found not guilty because he is legally insane—that is, his mental illness makes him incapable of understanding that what he did was morally wrong.⁹

If a defendant’s mental state meets the McNaghten test, it doesn’t matter whether it was a permanent condition or a temporary one—even if it lasted only a few hours. Temporary insanity qualifies for the California insanity defense just as a permanent mental condition does.¹⁰

Despite all this, the number of mentally ill criminal defendants who actually plead not guilty by reason of insanity is quite low. Nationwide, only about one percent (1%) of all criminal defendants assert the insanity defense.¹¹

Example: Elizabeth suffers from severe depression, a debilitating mental illness. She shoplifts clothes from an expensive boutique and is arrested and charged with petty theft.

Elizabeth’s depression caused her not to care about the consequences of the shoplifting. But it did not prevent her from understanding what she was doing. It also did not prevent her from understanding that the theft was morally wrong.

So even though Elizabeth’s mental illness contributed to her criminal activity, she was not legally insane when she shoplifted—and so she cannot assert the legal defense of insanity.

1.1. The McNaghten rule in California

California adopted the McNaghten rule as its legal definition of insanity when voters passed Proposition 8, known as the “Victim’s Bill of Rights,” in 1982.¹²

It is important to note that the California test for whether someone is legally insane only requires the defendant to prove that

• s/he was incapable of understanding the nature of his/her act OR 
• s/he was incapable of distinguishing right from wrong—not both.¹³

Example: Betty suffers from manic-depressive disorder. After filling up her gas tank, she drives away from the gas station without paying. A gas station attendant follows her on a motorcycle. Trying to escape him, Betty drives at over 80 mph and runs stoplights. Her reckless driving leads to an accident that kills another driver.

Betty is charged with vehicular manslaughter. She asserts the insanity defense. The jury decides that she WAS capable of understanding the nature of her actions—but was NOT capable of distinguishing right from wrong. Therefore, she is not guilty by reason of insanity.¹⁴

1.2. The insanity defense and drug addiction

Mental health problems and drug or alcohol addiction often go hand-in-hand. However, you may not assert the legal defense of insanity just because you

• Were addicted to drugs or alcohol when you committed the crime, or
• Had recently used drugs or alcohol when you committed the crime.¹⁵

Example: Jeffrey suffers from acid flashbacks due to his earlier extensive use of the drug LSD. These flashbacks cause him to hear voices that aren’t really there. When he is at a bar, he mistakenly believes that the bartender is threatening him and attacks the man. This leads to him getting charged with California assault.

Because Jeffrey’s delusions were due to the use of drugs rather than a non-drug-related mental condition, he cannot assert the insanity defense.¹⁶

However, if you were under the influence of drugs or alcohol when you committed a crime, the legal defenses of voluntary intoxication or involuntary intoxication may be of help to you.¹⁷

2. How do I prove insanity as a legal defense in California?

It is the defendant—and not the prosecutor—who bears what is called the “burden of proof” on the insanity defense.¹⁸

In most aspects of a criminal trial—including most importantly the basic question of guilt or innocence—the prosecutor has the burden of proof.¹⁹ But California’s insanity defense is what’s known as an “affirmative defense.”

As Riverside criminal defense lawyer Michael Scafiddi²⁰ explains:

“An ‘affirmative defense’ is essentially a claim which the defendant makes that says ‘even though I committed the crime, my conduct should be excused for the following reason….’ In the case of the insanity defense, the reason is the defendant’s mental condition when she or he committed the crime.”

With an affirmative defense such as insanity, it is the defendant who must prove that s/he

• was insane at the time of the crime and
• should therefore be excused from his/her criminal conduct.²¹

2.1. “Preponderance of the evidence” standard for the insanity defense

The defendant who pleads the insanity defense is required to prove that s/he was insane when the crime was committed by a “preponderance of the evidence. ”This means that s/he has to show that it is more likely than not that s/he was insane.²²

Contrast this to the “beyond a reasonable doubt” standard of proof that the prosecution has to meet when it comes to the defendant’s

• guilt or
• innocence.

“Beyond a reasonable doubt” means that the evidence is so strong that there is no logical explanation other than that the defendant is guilty.²³

Though even under the preponderance of evidence standard, if the jury feels that neither side has the stronger argument on the insanity defense. That is, if the evidence on both sides is equally strong—then they must rule against the defendant.²⁴

3. How do I enter a “not guilty by reason of insanity” plea in California?

There are two ways to pursue an insanity defense. You can either

1. Plead both “not guilty” and “not guilty by reason of insanity,” OR
2. Admit that you committed the crime but plead “not guilty by reason of insanity.”²⁵

3.1. Entering a “dual” plea of “not guilty” and “not guilty by reason of insanity”

The first way to enter a California insanity plea is to enter two pleas – one of “not guilty,” and a second of “not guilty by reason of insanity.”²⁶

The first “not guilty” plea means that you did not actually commit the crime with which you were charged. The second plea means that you are asserting that—even if you did commit the crime—you should not be convicted because you were insane when you did so.

If you enter a dual plea, you will make your way through the California criminal court process as follows:

1. The first step will be a trial that covers the question of your guilt/innocence—not the question of your sanity;
2. If you are found not guilty, you go free, and the case is over; BUT
3. If you are found guilty at this stage, the case proceeds to a hearing on your sanity that is called the “sanity trial.” This hearing may involve the same jury who ruled on your guilt/innocence, or a new jury. In the sanity trial, the court will decide whether you should be found not guilty by reason of insanity.²⁷

This process is what is called a “bifurcated trial”—because the question of your guilt and the question of your sanity are dealt with in two separate proceedings.

3.2. Sanity hearings in California

During the sanity hearing, the defendant presents expert witnesses—usually psychiatrists—who testify that at the time of the offense, the defendant either

1. didn’t understand the nature of his/her act, or
2. didn’t understand that the act was wrong.²⁸

These are the only issues that are relevant during the sanity trial.²⁹

If the jury decides unanimously that the defendant was insane when s/he committed the crime, then s/he will be found not guilty by reason of insanity.³⁰

The sanity hearing usually takes place before a jury—but not always. A judge may remove the issue of insanity from the jury if s/he feels that the defendant has failed to present sufficient evidence that they were insane when they committed the crime.³¹

Example: Victor is charged with aggravated California robbery. During his sanity hearing, he claims that he has suffered numerous blows to the head throughout his life—and that these have caused Satan to take over his body.

But the two psychologists who examine Victor testify that they believe he is making that up. The prosecution also presents a recording of a conversation in jail in which Victor tells his brother that he is “doing the homeless nut routine.”

The judge therefore concludes that there is not enough evidence that Victor is actually insane—and does not let the jury consider his insanity defense.³²

3.3. Entering a single plea of “not guilty by reason of insanity”

In some cases, a defendant and his/her attorney may decide that it makes the most sense not to bother with a standard “not guilty” plea. Instead, the defendant

• concedes that s/he is guilty of the offense and
• only pleads the insanity defense.³³

In these cases, the court proceeds directly to the sanity trial described in Section 3.2. There is no separate trial on guilt or innocence.³⁴

4. How does an insanity plea affect sentencing?

If you successfully plead the insanity defense, then you will not receive the normal jail/prison sentence for your crime. Instead, you will be committed to a state mental hospital.³⁵

There are two reasons for commitment:

1. to rehabilitate and treat the defendant, and
2. to protect the defendant and society from further harm.³⁶

The defendant must remain in the state mental hospital until:

1. doctors believe that s/he has regained sanity,
2. the maximum term of imprisonment for that crime has expired, or
3. doctors believe s/he would do well in an outpatient treatment program instead.³⁷

Additional resources

For more in-depth information on the insanity defense, refer to the following scholarly articles:

• Mentally disordered offenders and the law: Research update on the insanity defense, 2004–2019 – International Journal of Law and Psychiatry.
  
• “The Angels That Surrounded My Cradle”: The History, Evolution, and Application of the Insanity Defense  – Buffalo Law Review.
  
• Not Guilty, Yet Continuously Confined: Reforming the Insanity Defense – American Criminal Law Review.
• Kahler v. Kansas: The End of the Insanity Defense? – Duke Journal of Constitutional Law and Public Policy.
• Sentencing Alternative to an Insanity Defense – Seattle Journal of Social Justice.

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