On January 20, 1843, Daniel M'Naghten, a Scottish woodturner suffering from severe paranoid delusions, shot Edward Drummond, the personal secretary to British Prime Minister Sir Robert Peel. M'Naghten mistakenly believed Drummond was Peel himself, whom he blamed for persecuting him. Drummond died days later, and M'Naghten was charged with murder.
During the trial at the Old Bailey, the defense argued that M'Naghten was overcome by a disease of the mind that deprived him of moral control over his actions. Medical experts testified to his extreme paranoia, leading the jury to return a verdict of not guilty by reason of insanity. Public outcry was swift, and Queen Victoria herself expressed outrage over the acquittal, prompting the House of Lords to pose a series of hypothetical questions to the highest judges of England to clarify the law on criminal responsibility.
The resulting answers formed the M'Naghten Rules. Under this landmark standard, to establish an insanity defense, it must be clearly proved that at the time of committing the act, the accused was laboring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing, or, if he did know it, that he did not know he was doing what was wrong. This strict cognitive test became the foundational standard for criminal insanity across common law jurisdictions worldwide.