Who Decides the Sanity of a Defendant in CA? California's Insanity Defense

In California criminal proceedings, questions about the defendant's mental health or mental state can play a very important role. Many people assume that a judge or doctor will decide if a person is legally insane or not before they stand trial, but the reality is that it is much more complex. There is a specific process in California's criminal justice system that determines sanity, and many people are involved. This is important to understand for anyone who is considering this as a legal defense.

Legal Insanity vs. Mental Illness in a Criminal Case

Before we look at who decides sanity in California, it's important to know the difference between mental illness and legal insanity. A person may have a mental health condition, they may have been given mental health treatment, and they may even have spent time in a mental hospital or in outpatient treatment for a mental condition. This, however, doesn't mean that they can use an insanity defense.

In California both the prosecution and defense follow a modified version of the M'Naghten Rule. This is a standard where a defendant is found to be legally insane only if, at the time of the criminal act, they were not able to understand the nature of their crime, or understand that the act was morally wrong. Goss Law can share insight on M'Naghten Rule vs. Model Penal Code.

The Judge’s Role in Sanity Determinations

A judge will play a very important role in an insanity defense case, but they do not necessarily decide a defendant's sanity. Instead, the judge ensures that the legal process is done correctly, they rule on motions, and then determine, after the defense presents evidence, if an insanity defense can proceed.

When a defendant chooses to enter a plea of not guilty by reason of insanity, the judge will evaluate whether or not the plea is legally proper and if psychiatric evaluations are required. The court may ask for a sanity trial, they may consider any time in a treatment facility, they might look at the defendant's criminal history, or even consider the outpatient status of any current mental health treatment. However, unless there are very limited circumstances, a judge, alone, will not determine sanity.

The Jury’s Central Role in Deciding Sanity

In almost all criminal cases in California where a defendant's competence and mental state are in question, the jury will make the ultimate decision. When a criminal defendant pleads insanity, there is a bifurcated trial system.

First, the jury will determine if the defendant committed the underlying crime, and then the same jury will determine if the defendant was legally insane under California law at the time of the crime.

In trial court, during the sanity trial, jurors will hear testimony from experts, they will review medical records, and they will consider any other evidence that may have affected the defendant's mental health status at the time of the crime. Only then would there be a successful insanity defense.

It's also important to consider this, too - even if multiple mental health professionals believe that a defendant was legally insane, the jury doesn't have to agree.

Psychiatric Experts and Their Influence in Legal Defense

Psychiatrists and psychologists play a critical role in insanity cases, but they do not decide sanity. Instead, they provide expert opinions that inform the jury’s decision.

Court-appointed experts, defense experts, and prosecution experts may all evaluate the defendant. These evaluations typically involve clinical interviews, psychological testing, review of medical records, and analysis of the defendant’s behavior at the time of the offense. Experts then testify about whether the defendant met the legal criteria for insanity.

While expert testimony is often persuasive, it is not binding. Jurors are free to accept or reject expert opinions, particularly if they believe the defendant’s actions demonstrate awareness, planning, or consciousness of guilt. For legal guidance, our criminal law firm in Sacramento may be able to help.

The Burden of Proof for Mental Health Issues Rests With the Defendant

In California, the defendant bears the burden of proving insanity. This is a key distinction from most criminal trials, where the prosecution must prove guilt beyond a reasonable doubt. For an insanity defense, the defendant must prove legal insanity by clear and convincing evidence.

This higher burden means the jury must be firmly convinced that the defendant met the legal insanity standard at the time of the offense. Any evidence suggesting the defendant understood their actions or knew they were wrong—such as fleeing the scene, hiding evidence, or making incriminating statements—can undermine the insanity claim.

What Happens in a Bench Trial with a Judge?

In rare cases, a defendant may waive the right to a jury trial. When this occurs, the judge acts as the trier of fact for both the guilt and sanity phases. In these situations, the judge decides sanity instead of a jury.

Bench trials involving insanity defenses are uncommon because of the complexity and high stakes involved. However, they may be used strategically in certain cases, depending on the facts, the legal issues, and defense counsel’s assessment of the forum.

What Happens if Someone is Found Not-Guilty by Reason of Insanity?

If a jury or judge finds a defendant not guilty by reason of insanity, the defendant is not released. Instead, the court orders commitment to a state mental health facility, such as a California State Hospital.

The commitment period can last as long as—or longer than—the maximum prison sentence the defendant would have faced if convicted. Release occurs only after medical professionals and the court determine that the individual no longer poses a danger. Periodic hearings are held to assess progress and continued confinement.

Why Sanity Determinations Are So Challenging

Sanity determinations are among the most difficult decisions juries are asked to make. Jurors must evaluate complex psychiatric testimony while applying a strict legal standard that differs from everyday understandings of mental illness.

Prosecutors often argue that purposeful actions, planning, or post-crime behavior demonstrate sanity, while defense attorneys emphasize cognitive impairment and lack of moral understanding at the time of the offense. The outcome often depends on how clearly the evidence connects the mental condition to the defendant’s ability to understand their actions during the crime.

The Importance of Skilled Criminal Defense Representation

Because juries ultimately decide sanity in most cases, effective presentation of evidence is critical. Insanity defenses require coordination between legal strategy and medical expertise, strict compliance with procedural rules, and careful jury education.

An experienced California criminal defense attorney can evaluate whether an insanity defense is appropriate, identify qualified experts, and present the evidence in a way that aligns medical findings with legal standards. Poorly presented insanity claims can fail quickly and may weaken other defense options. They can also explain temporary insanity: when it applies and how it works in CA.

Reach out to Goss Law if you or your family member is facing charges in California and you believe that a person's sanity or mental defect played a role. Goss Law understands the California court system and how felony cases can be affected by a temporary insanity or insanity defense. Legal help is available 24/7.