Diminished Capacity

Diminished capacity is a legal defense used by a defendant to argue that, while he admits to having broken the law, he should not be held fully criminally liable due to his “diminished” mental state at the time. Diminished capacity is a partial defense, which requires the defendant to have committed the crime while in a very specific state of mind. For example, diminished capacity might be used as a defense if the defendant had suffered a head injury, which rendered him incapable of premeditating the murder he committed. To explore this concept, consider the following diminished capacity definition.

Definition of Diminished Capacity


  1. A legal defense wherein a defendant admits his guilt, but argues that he should not be held fully liable for his actions due to his diminished mental state at the time.

Diminished Mental Capacity

A diminished mental capacity plea is different from the similar “not guilty by reason of insanity” plea. Someone who pleads a “by reason of insanity” defense, if successful, will receive a “not guilty” verdict. He will also be ordered by the court to be confined to a mental hospital. Someone who is victorious on a diminished mental capacity plea, however, will simply be convicted of a lesser offense. The diminished mental capacity plea is based on the idea that certain people are incapable of being in the required mental state necessary to commit a particular crime.

The diminished capacity plea is often seen in cases involving murder or manslaughter. In these very serious crimes, it is important to distinguish whether or not the defendant was capable of intending to cause the victim’s death. If not, then the defendant will be convicted of causing the death recklessly, rather than intentionally. If the defendant is successful on his diminished capacity plea, then his charge will likely be knocked down from murder to manslaughter, and he will receive a lighter sentence as a result.

An example of diminished capacity can be a person’s lower-than-average intelligence. For instance, a full-grown man who possesses a childlike mental state can be deemed mentally impaired, and therefore incapable of knowingly committing, or of premeditating, an attack on his victim. In this case, the only reasonable verdict is manslaughter.

Criminal law requires that a defendant’s conduct be voluntary for him to be prosecuted to the fullest extent of the law. In the case of diminished capacity, however, the person’s mental state interfered with his ability to decide whether he would break the law.

The reason why someone suffering from an impaired mental state can still receive a conviction, however, as opposed to an acquittal, is because the law aims to be fairly balanced. On one hand, it is unfair to convict someone with a harsher sentence when he is incapable of committing the crime with which he is charged. On the other hand, there is still the duty that is owed to society, in that the general public is kept safe from those who are incapable of controlling their own behavior.

Diminished Capacity Defense

In order for someone to be guilty of first-degree murder, the state must be able to prove beyond a reasonable doubt that he premeditated, or pre-planned, the attack. He also must have deliberately murdered the person, having intended to commit murder all along. Those three elements are required for a first-degree murder conviction. If there is evidence that proves that the defendant’ mental state rendered him incapable of carrying out any of these three elements, then the state cannot convict him of first-degree murder and the defendant’s diminished capacity defense is a success.

Of course, unlike being found guilty by reason of insanity, when a defendant is found guilty of murder with diminished mental capacity, he is not acquitted. In such an example, a diminished capacity defense may secure him a conviction of second-degree murder instead. A second-degree murder charge only requires that the defendant acted with general malice when he killed his victim.

When a defendant employs a diminished capacity defense, the state is responsible for proving that the defendant was capable of committing the crime with which he was charged. By contrast, with a not guilty by reason of insanity defense, then the burden of proof is on the defendant to prove that he was, in fact, suffering from insanity – as defined by the law – when he committed the act.

Diminished Capacity Example Involving the “Twinkie Defense”

Dan White was a former police officer and firefighter for the city of San Francisco. He and Harvey Milk were both elected to their city’s Board of Supervisors in 1977. Upon his election, White resigned from his higher-paying job with the fire department to serve on the Board, due to the fact that the city charter prohibited employees from holding two city jobs at the same time.

White soon became frustrated with the city’s politics and resigned from his position in November of the following year. He was also experiencing stress related to the financial difficulties that resulted from his lower salary, and the failure of a restaurant that he had opened. Mayor George Moscone soon appointed White’s replacement, but due to the support and promised financial backings of his supporters, it wasn’t long before White realized that he wanted his old job back.

Milk and several of the city’s other leaders lobbied hard against White’s reappointment. In Milk’s case, his reason for fighting back against White’s reappointment was because the two had clashed on political issues in the past. On November 27, after White met with Mayor Moscone at his office at City Hall, his request for reinstatement was rejected yet again. White then shot and killed Moscone. He then took the time to reload his revolver – a move that would later be considered evidence of his intent to murder Milk, especially considering how White had brought extra ammunition along with him.

After leaving Moscone’s office, White ran into Milk, who agreed to join him inside White’s former office. White then shot Milk several times and fled the scene. He ultimately turned himself in to his former co-workers at the precinct where he formerly worked, and recorded a statement acknowledging the shootings, but denying premeditation. White was charged with first-degree murder with special circumstance, a crime that carried the death penalty upon conviction.

White’s defense team argued that he was depressed, and that proof of this could be found in, among other things, White’s mainly junk food diet. The media went on to report this inaccurately, stating that White’s consumption of junk food had caused his mental state, not that it was a symptom of it. This led to the birth of the term “Twinkie defense,” which has since become legal slang.

White’s team also argued that his depression caused him to suffer from a mental state of diminished capacity, which would have rendered him incapable of premeditation, which is necessary to commit first-degree murder. The jury agreed, and upon the conclusion of his criminal trial, White was convicted of voluntary manslaughter, as opposed to first-degree murder.

Many were outraged by this verdict, believing that White literally got away with murder. Not only did he bring extra bullets with him, but he also deliberately avoided the City Hall metal detectors by climbing through a window. White shot Moscone multiple times – in the shoulder, in the chest, and twice in the head – before reloading his .38 revolver, walking across City Hall, and shooting Milk five times.

Many individuals in the gay community believed that, because Milk was openly homosexual, the jury may have been homophobic, and were therefore willing to give White a lesser sentence. San Francisco Weekly referred to White as “perhaps the most hated man in San Francisco’s history.”

While California had been the first state to allow a diminished capacity defense, White’s case led the state to abolish its recognition.

In 1998, Frank Falzon, a homicide detective with White’s former precinct, told the press that he had met with White in 1984, upon White’s early release on parole. Falzon had been a friend of White’s, and he had taken White’s statement when he turned himself in.

Falzon reported that during their meeting, White not only confessed to premeditating the murders, but that he had also planned to kill two additional people. Falzon added that White had never once expressed remorse for the murders, and that he believed White’s confession. White committed suicide less than two years later.

Related Legal Terms and Issues

  • Beyond a Reasonable Doubt – The standard of proof required in a criminal trial: that no other logical explanation exists, given the facts presented, that the accused committed the crime.
  • Criminal Charge – A formal accusation by a prosecuting authority that an individual has committed a crime.
  • Defendant – A party against whom a lawsuit has been filed in civil court, or who has been accused of, or charged with, a crime or offense.
  • Jury – A group of people sworn to render a verdict in a trial, based on evidence presented.
  • Intent – A resolve to perform an act for a specific purpose; a resolution to use a particular means to a specific end.
  • Victim – A person who is injured, killed, or otherwise harmed as a result of a criminal act, accident, or other event.