Insanity Defense - Mitigating Factors and Diminished Capacity

Mitigating Factors and Diminished Capacity

The United States Supreme Court (in Penry v. Lynaugh) and the United States Court of Appeals for the Fifth Circuit (in Bigby v. Dretke) have been clear in their decisions that jury instructions in death penalty cases that do not ask about mitigating factors regarding the defendant's mental health violate the defendant's Eighth Amendment rights, saying that the jury is to be instructed to consider mitigating factors when answering unrelated questions. This ruling suggests specific explanations to the jury are necessary to weigh mitigating factors.

Diminished responsibility or diminished capacity can be employed as a mitigating factor or partial defense to crimes and, in the United States, is applicable to more circumstances than the insanity defense. Where it is a partial defense, it has the effect of reducing the charge to manslaughter. The Homicide Act 1957 is the statutory basis for the defense of diminished responsibility in England & Wales, whereas in Scotland it is a product of case law. The number of findings of diminished responsibility has been matched by a fall in unfitness to plead and insanity findings (Walker, 1968). A plea of diminished capacity is different from a plea of insanity in that "reason of insanity" is a full defense while "diminished capacity" is merely a plea to a lesser crime.