How Can Someone’s Mental Health Impact a Criminal Case?

Unfortunately, there remains a high degree of stigma toward mental health differences in the United States, despite the statistical commonality of the occurrence. Mental health concerns can arise at any place in the judicial process, and how these interact with life events can be deeply complicated.

If you’ve been accused of a crime and you believe a mental health issue you have is relevant to the matter, you will likely need an expert witness like a psychiatrist or psychologist to testify. This is why having an experienced and knowledgeable Red Bluff criminal lawyer on your side is very important. In this article, we will cover some situations the mental health of the defendant has been considered legally relevant.

Context #1: Determining Your Competency

A core principle of American jurisprudence is that someone cannot be tried or punished if they are mentally incompetent. The terminology itself shows the ableist perspective of ages past in which our laws are steeped, as the language of competence and incompetence carries the implication of lesser worth. In any case, a mentally incompetent defendant is one who, because of a mental disorder or developmental disability, can’t understand what is happening during criminal proceedings or can’t assist their counsel in setting forth a rational defense.

When deciding cases involving questions of competency, often what is being alleged is that a trial abused its discretion when it refused to order a competency hearing. Regardless of the presence of expert testimony, if a defendant shows substantial evidence that they cannot help their counsel with a rational defense, courts are obligated to stop the proceedings and instead begin competency hearings. Substantial evidence means evidence that shows a reasonable doubt about the defendant’s irrational behavior, their demeanor in court, or any previous medical opinions on the defendant’s competence, among other factors.

Defunct Context #2: Your Mental Health Means You Couldn’t Form the Required Intent

In the past, California recognized a plea called diminished capacity, which stated that someone was unable to have the mental state that a specific intent crime required. Unlike insanity, which is an affirmative defense that ends in the defendant being committed, diminished capacity typically results in a conviction of a lesser offense. For example, under a diminished capacity plea, a lawyer might argue that the defendant was not capable of intending to kill the victim, such that at worst, they were only guilty of manslaughter for killing the victim recklessly.

California began to permit the diminished capacity plea in the 1950s, until 1982. The 1979 California v. White case involved a former city supervisor who killed the mayor of San Francisco and another city supervisor. Although the crime showed a lot of premeditation such as the defendant packing extra bullets, the court accepted the argument that consistently eating junk food like Twinkies had imbalanced the chemicals in the defendant’s brain, such that his subsequent depression made him unable to premediate murder, a requirement for first-degree murder. Instead, the court found the defendant guilty of the lower charge of voluntary manslaughter. The uproar over this decision led to the approval of a California proposition to remove the “Twinkie defense,” as it was called.

Although the diminished capacity plea no longer exists, California Penal Code Sections 28 and 29 allow defendants to introduce evidence of mental illness when an element of the charged crime is that someone has in fact formed a specific mental state. Expert witnesses are not allowed to comment on whether someone could have the mental capacity to form a specific mental state or whether the defendant in question did form such a state. That is, the expert witness cannot say they believe a defendant couldn’t or didn’t premeditated or deliberate. An expert witness can, however, say that the defendant had a mental illness that would cause them to act impulsively without acknowledging or considering the consequences of their actions.