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Diminished Capacity Defense


The concept of diminished capacity defense (hereinafter referred to as DCD) is traditionally associated with California. California allowed the DCD plea in 1950s, but the defense was scrutinized intensely during the People v. White case in 1979, often refereed to as the Twinkle Defense. In line with this jurisdiction, DCD is understood to be illustrating that a defendants mental statures was contracted by intoxication, mental defect, or mental illness. Similar to insanity defense, DCD examines the mental capacity of the defendants at the time of antisocial acts that they have been charged with as crimes. According to the Legal Information Institute LII, the defense is also similar to the insanity defense in the sense that that evidence related to mental illness must be produced, but differs in the sense that DCD does not required the respondent to be able to reason between right or wrong. Historically, the challenge of negating mens rea in capital offenses is attributed to the fact that customary doctrine demanded that defendants acts (mistakes) had to be objectively meaningful, but the mistakes produced by mental defects are subjective and unreasonable. The unfairness of the traditional doctrines compelled courts to accept diminished capacity defense. Ideally, fairness or justice should permit defendants to use relevant evidence to negate the prosecutions case when conviction is at stake.

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Model Penal Code: Diminished Capacity Defence

Under certain circumstances, the criminal law partially or completely excuses actors whose ability to response to reasons lack the substantial capacity to reason are partially or completely diminished. For instance, if a person lacks the capacity to respond to reasons and as of consequence the ability to conform personal conduct to the basic requirements of law because of mental defect or disease, the actor may be excused in some jurisdictions on grounds of insanity. As pointed by Burkhart and Stein, criminal defendants have the right to introduce any evidence relevant to the mens rea issue.

Case Studies

People vs. White. In 1979, Daniel James White, a defendant in the People v. White case successfully used the diminished capacity defense, where he was convicted of voluntary manslaughter instead of murder. White shot and killed San Francisco Supervisor Harvey Milk and Mayor George Moscone. The defendant shot the two victims during the day, but got lesser sentence because his trial presented a successful DCD. A number of psychologists provided evidence for the defense, whereby it was argued that defendant was suffering from severe depression at the time of the crime.

No premeditation. The defense also argued that the depression (mental condition) rendered the defendant unable to premediate the assassination of Milk and Moscone. As argued by the defense side, White shot the two victims due to heat of passion and no deliberation. The concept of irresistible impulse elevated depression in Whites case contrasts the concept of premeditation, which is a test for first-degree murder. Illustrating that an irresistible impulse led to the shooting negated the idea of remediation, leading to voluntary manslaughter.

Involuntary manslaughter. Grounded on the defense testimony, the defendant was convicted for voluntary manslaughter. Voluntary manslaughter means that the shooting by White as intentional, but the defendant did not have a prior intent to shoot and kill the two victims. The circumstances resulting to the shooting and loss of life (depression) must have been the type that could cause someone reasonable to be mentally disturbed or emotionally unstable; otherwise, the shooting and loss of life could have been treated as first-degree murder. From a legal perspective, involuntary manslaughter refers to unintentional killing due criminal negligence or recklessness or from an antisocial act that is of low-level felony. The main difference between voluntary and involuntary manslaughter is that the loss of life in the latter is unintended. Under involuntary manslaughter, the killing is without criminal intent or malice aforethought. In the People v. White case, the DCD was used a mitigating defense, in the sense that the defense had the burden of establishing that the defendant was not guild of fist- or second-degree murder because of diminished capacity. As of consequence, the defendant automatically was guilty of committing a lower degree (voluntary manslaughter) of murder.

Types of tests used. Individuals culpable for their antisocial acts should ideally be punished by the legal system. The prosecution must be able to prove that the crime meets two elements: forbidden act (actus reus) and guilty of mind or mens rea. According to Testa and Friedman, the definition of crimes included not only what constitutes them, but also the level of mens rea. Under DCD, the burden of the defendant is to prove that there was no mens rea. Therefore, if the prosecution in the People v. White case could prove that White shot and killed the two victims intentionally, as well as that he had the knowledge that his act would result in their death, then the prosecution would have proven mens rea for the crime. There are elements that the defense must satisfy for the defendant to qualify for involuntary manslaughter. The first test is that the defendants actions led to loss of life. Secondly, the defendants actions should have been reckless disregard of the victims life or innately dangerous to the victim. In addition, the defendant must have known that his or her actions were a threat to the life of the victim. In agreement with Aikin, Whites case met the voluntary manslaughter threshold because despite shooting and killing the two victims, White had no malice aforethought. In other words, there was no deliberation to shoot and kill the victims. As argued by the defense side, the irresistible emotion that normal reasonable people could experience under the same circumstances led to the shooting. To recap, the People v. White case findings flow logically with the definition of DCD. The defendant proved that at the time of the shooting his mental capacity was unable to form the vital mens rea.

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Mens Rea

DCD refers to either mens rea variant or the partial excuse variant. In regards to mens rea variant, the defense is required to introduce evidence of mental defect to negate the guilt of mind (premeditation) required by a specific crimes definition. On the other hand, the partial excuse variant entails the use of mental defect evidence to support an affirmative defense. The nonappearance of mens rea is similar with diminished capacity defense in some aspects. Conceptually, mens rea and diminished capacity overlap and where the latter is allowed as an excuse, it is at time referred as the nonexistence of mens rea. However, these thinking have been distinguished in some ways. For example, an actor may invoke a mens rea defense to negligent shooting, but a diminished capacity defense for the same crime may be difficult because any criminal awareness below criminal negligence is not a crime. In simple terms, DCD and insanity defenses are distinct from one another.

Culpability. Legal guilt, also known as culpability for committing a crime demands that prosecution beyond reasonable doubt proves both the affirmative defense and definitional elements of the charged crime. Affirmative defense includes the excuse of duress and legal insanity. The diminished capacity doctrine allow defendants to avoid criminal liability by demonstrating that their mental capacity was contracted to the extent that they could not have premeditated the crime they are charged with. In other words, the burden of the defendant is to prove that their mental impairment at the time of the crime was the main contributory factor. In line with the Supreme Court explanation, DCD allows defendants to introduce mental abnormality-based evidence at trial for two reasons. The first reason would be to negate the mental aspect of the offense; hence, exonerating the respondent of that charge. On the other hand, defendants adopt the doctrine of capacity defense to reduce the degree of the charge for which they are likely to be convicted. In essence, DCD applies to respondents lacking the necessary guilt of mind (mens rea) to commit a serious with the intent and knowing purpose required for it.

Mental conditions. Parry and Drogin observed that most jurisdiction were not allowing diminished capacity defenses, and for that reason, related cases were declining steadily. As of 2007, only Oregon, Iowa and New Mexico had some form of the traditional DCF. Following the decline in diminished capacity cases, there has been calls for its alternative, which recognizes a categorical DCF for capital crimes committed by individuals with mental retardation. This approach applies in the prohibition of the death penalties for individuals with mental disabilities. Trauma- exposed individuals persons with posttraumatic stress disorder (PTSD) might present a DCD by claiming that their PTSD attack impaired the mental state required for the offense they are charged with, especially murder. DCD is supported by a series of California cases and by due process.


Reasons for DCD. Prior to the adoption of either mens rea or partial excuse variants of DCD, defendants suffering from intoxication or mental defect at the time of the crime could not use such evidence as a mitigation defense either by establish an affirmative defense or by negating the prosecutions case. One of the reasons for diminished capacity defense is that the insanity excuse is limited in the sense that it is only available for actors if their diminished capacity to reason was caused by a mental defect or disease. It follows that actors who did not have the intent to commit a crime because their mental status or reasoning capacity was partially diminished at the time of the crime cannot use the insanity defense. The other reason for diminished capacity defense is that this affirmative defense may result in lesser criminal charge for actors that have reduced culpability that is not enough to establish an insanity defense or mens rea. Lastly, DCD ensures that the crime for which defendants are convicted accords with their mental state.

Reasons against DCD. Diminished capacity defense is only available for actors as a partial defense to murder. While it negated that the mens rea that should be present for serious crimes, DCD does not prove insanity. In addition, the defense is available in few jurisdictions and restricted to specific intent crimes, murder in particular. Furthermore, burden of proof of insanity has been left by the federal system and many states on the defendant because of lack of public confidence, problems of proof and safety. For this reason, it is unwise to adopt a DCD, which would place the burden of proof on the prosecution for most mental illness issues. While a successful DCD result in conviction of the defendant for a lesser offense, it does not result in acquittal as in most insanity defenses.

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