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This doctrine recognizes that although, at the time the offense was committed, an accused was not suffering from a mental disease or defect sufficient to exonerate him or her from all criminal responsibility, the accused's mental capacity may have been diminished by intoxication, trauma, or mental disease so that he or she did not possess the specific mental state or intent essential to the particular offense charged.
n. essentially a psychological term which has found its way into criminal trials. A contention of diminished capacity means that although the accused was not insane, due to emotional distress, physical condition or other factors he/she could not fully comprehend the nature of the criminal act he/she is accused of committing, particularly murder or attempted murder. It is raised by the defense in attempts to remove the element of premeditation or criminal intent and thus obtain a conviction for a lesser crime, such as manslaughter instead of murder. While the theory has some legitimacy, at times juries have been overly impressed by psychiatric testimony. The most notorious case was in People v. Dan White, the admitted killer of San Francisco Mayor George Moscone and Supervisor Harvey Milk, who got only a manslaughter conviction on the basis that his capacity was diminished by the sugar content of his blood due to eating "twinkies." (See: insanity, M'Naughten Rule)