Last Updated on February 12, 2025
In movies and TV shows, lawyers are constantly arguing that their clients are not guilty by reason of insanity to allow their obviously guilty clients to spend time in an institution before quickly being shuffled back into the public. In reality, though, the insanity defense is used in less than one percent of criminal trials and is only successful in around 30 trials per year. There are many reasons the insanity plea is utilized so rarely, starting with the difficulty of meeting the M’Naghten standard required under California Law. Beyond that, though, few people would even benefit from using the defense, even if their efforts are successful.
What is the Insanity Defense?
When someone pleads “not guilty by reason of insanity,” they are arguing that while they may be guilty of the crime, they should be found not guilty because, at the time the crime took place, they did not know what they were doing or that they were doing something wrong.
Pleading insanity is not the same thing as determining someone’s competency to stand trial, which is based on someone’s mental state at the time of their trial. In contrast, the insanity defense in criminal law cases is based on the person’s mental state when the crime occurred.
Another significant difference is that the insanity defense depends on a person’s cognition, meaning their ability to reason and problem-solve. On the other hand, competency to stand trial can be based on a person’s cognition or mental capacity, meaning their ability to recall events or communicate their decisions.
If a person is incompetent to stand trial, the trial will be postponed until they are declared competent. However, if a person is found not guilty by reason of insanity, they will be committed to a mental health facility until they have fully recuperated.
What Happens When Someone Successfully Pleads Insanity?
A common misconception is that those who are found not guilty due to insanity are then freed and allowed back on the street without serving any time for the offense they committed. But those who use this defense successfully are instead confined in a mental facility until they are deemed to no longer be a threat to themselves or the public.
In fact, studies have shown that those who are committed as a result of an insanity defense in criminal trials tend to spend more time confined in a mental health facility than those found guilty and sentenced to prison for the same crime. This increased penalty is the main reason most attorneys won’t even consider pleading insanity unless their client is facing life imprisonment or the death penalty.
Proving Insanity at the Time of the Crime
When it comes to defendants successfully using the insanity defense, California Penal Code section 1026 (PC) requires jurors to use the M’Naghten Rule (alternatively called the McNaughten rule). This standard requires the jury to presume the defendant is sane until their attorney proves otherwise. The M’Naghten Rule essentially means that when the crime was committed, the defendant had some type of mental disease or defect that showed they were incapable of knowing or understanding the nature or quality of their actions or from being able to distinguish between right and wrong.
As an example, this defense could possibly work for Dr. Jekyll once he no longer controls himself without taking his serum because he enters a state where he is incapable of knowing what his alter ego is doing. Notably, the insanity plea cannot be used in California when someone is voluntarily intoxicated though, so it would not apply if someone were to start committing crimes while high on mushrooms, for example.
Pros and Cons of Insanity Pleas
While the insanity defense is a very commonly discussed legal principle, there’s a reason few attorneys attempt to use this excuse to defend their clients. Some advantages to using this defense include:
- It can help clients avoid time in prison. For those who could genuinely benefit from mental health services, confinement in a facility focused on psychology can be preferable to time in prison.
- It allows defendants to avoid the death penalty. In cases that could result in the death penalty, the insanity defense can help clients avoid this most serious punishment.
- It provides some closure to the victim and their family members. Victims and their loved ones often want to hear the accused party accept responsibility for their actions and provide some justification for their wrong acts. By admitting guilt and explaining that they were not in their right mind at the time, the defendant can help the victims move on from the act.
- It protects the mentally ill from punishment for actions they do not comprehend. While someone who may commit criminal acts may be able to benefit from mental health treatment, they may not understand why they are put in prison. The insanity defense helps protect these vulnerable members of our society from being punished for actions they don’t understand.
While the pros to the insanity defense may benefit both individuals and society as a whole, the cons mostly only apply to the defendant. Here are some disadvantages to pleading insanity:
- The burden of proof is on the defense. Due in part to the media’s frequent depiction of the insanity defense as primarily serving as a way for guilty people to avoid prosecution, juries are hesitant to accept that a defendant is insane. Additionally, the law places the burden of proof of the victim’s insanity on the defense, making this strategy difficult.
- Proving insanity can be expensive. This defense strategy can be pretty pricey because it requires hiring psychologists and other expert witnesses.
- A successful defense still results in confinement. Worse still, because this confinement lasts an indeterminate period, defendants typically spend more time in mental health facilities than they would have spent in prison.
- Failure can be catastrophic. Statistics also show that when the insanity defense is used unsuccessfully, sentences tend to be longer than they would have been if the defense was not invoked. Arguing you don’t deserve to be sent to jail can be difficult when you’ve already admitted your guilt.
A Real-Life Example
While these cases are rarely used and even rarely successful, there are occasional situations where the defense is used —typically when the alternative is life imprisonment. In 2025, a judge determined a man was insane at the time he entered a stranger’s apartment and stabbed them over 4o times. The defendant said he was hearing voices and thought he was breaking out of a digital simulation with the attack. He was convicted of second-degree murder and sentenced to 15 years to life in a state hospital.
In most cases, it is often best to have your attorney negotiate a plea bargain to minimize the sentence you may face. If you have any questions about the insanity defense, please call (760) 643-4050 or (858) 486-3024 to schedule a free initial consultation with top defense attorney Peter M. Liss.
