Diminished Responsibility

Diminished Responsibility

Diminished responsibility is a defence created by statute for use against a charge of murder; it does not exist at common law. 

Under section 3(1) of the Homicide Ordinance (Cap. 339): where a person kills or is a party to the killing of another, he shall not be convicted of murder if he was suffering from such abnormality of mind (whether arising from a condition of arrested or retarded development of mind, or any inherent causes, or induced by disease or injury) as substantially impaired his mental responsibility for his acts and omissions in doing or being a party to the killing. 

In relation to this defence, an English court stated in one case that:  

1. To satisfy the defence, the defendant must prove: 

• that he was suffering from an "abnormality of mind" at the time of the offence; 
• that this abnormality of mind arose from an internal cause such as arrested development of mind, or from disease or injury; and that it seriously affected his mental responsibility at the time of the killing. 

2. "Abnormality of mind" refers to a state of mind so different from that of ordinary persons that a reasonable person would regard it as abnormal. This concept is a wide one, covering the ability to perceive things; the ability to judge whether conduct is right or wrong; and the ability to control one's conduct in accordance with rational judgment. "Mental responsibility for one's acts" refers to the degree of a person's mental responsibility for his own conduct, including whether he is able to exercise willpower to control that conduct.  
3. Whether the defendant was suffering from an "abnormality of mind" at the time of the killing is a matter for the jury. Medical evidence is important, but the jury may also consider other evidence, such as the defendant's conduct, words and demeanour. If the other evidence is more persuasive, they need not accept the medical opinion in full. As to the cause of the abnormality of mind (such as disease or injury), expert evidence is generally required.  
4. If the jury is satisfied that the defendant was suffering from an abnormality of mind arising from a qualifying cause, they must still decide whether that abnormality was "substantial" enough to impair his mental responsibility. This is a question of degree, ultimately to be decided by the jury. Medical evidence is of assistance, but the jury may differ from the medical opinion. 

5.  There is a difference between "the defendant did not resist the impulse" and "the defendant could not resist the impulse". This distinction is of critical legal importance, because the two carry entirely different legal consequences. "Did not resist the impulse" means that the defendant was objectively capable of resisting but chose not to—this is mere weakness of will and is insufficient to support the defence, so the defendant remains fully liable for murder. Conversely, "could not resist the impulse" means that, owing to an abnormality of mind, the defendant's willpower was substantially impaired so that he was simply unable to control his conduct—this may form the basis of a defence of diminished responsibility, reducing murder to manslaughter. 

   The leading authority on this distinction is R v Byrne [1960] 2 QB 396. The defendant, Byrne, was a sexual psychopath who, being unable to control his powerful perverted sexual urges, strangled and mutilated a young woman. The trial judge directed the jury that if the defendant merely experienced, from time to time, abnormal sexual urges that were difficult to resist, the defence of diminished responsibility did not apply, and Byrne was convicted of murder. The Court of Appeal overturned the conviction, holding that the trial judge's direction was wrong—the definition of "abnormality of mind" is wide enough to cover the situation where the defendant is unable to exercise willpower to control his conduct, and is not confined to impairment of the cognitive or rational faculties. The murder conviction was accordingly substituted with one of manslaughter. 

   In other words, if the defendant was capable of resisting but chose not to, the defence of diminished responsibility does not succeed and murder is established; if the defendant was unable to resist owing to an abnormality of mind, the defence may succeed and murder may be reduced to manslaughter. 

   Science cannot precisely distinguish this difference, nor measure the degree of difficulty a person has in controlling an impulse. These are questions that can only be decided by the jury using common sense. The courts have repeatedly emphasised that the phrase "mental responsibility substantially impaired" describes a state of mind that, in ordinary language, is close to "partial insanity" or being "on the borderline of insanity". 

6. If the abnormality of mind rendered the defendant wholly unable to control his conduct, then, provided the cause is a qualifying one, this is sufficient to establish the defence. Even if it was merely "very difficult to control", the defence may still be made out, provided the degree of difficulty was high enough. 

The defendant bears the burden of proving diminished responsibility on the "balance of probabilities". The issue should be raised by the defendant. Even where there is evidence suggesting the possible existence of diminished responsibility, the judge should generally not leave the issue to the jury unless the defendant has first raised it. 

If the defendant successfully relies on diminished responsibility as a defence, the range and nature of the penalties or orders that may be imposed extend from a probation order to life imprisonment. The court may make a hospital order, which may be for a fixed or an indefinite duration.