The M'Naghten Rule

Daniel McNaughten was charged with the murder of Edward Drummond, a secretary to Prime Minister Robert Peel. On January 20, 1843, Drummond was returning, alone, to 10 Downing Street after running an errand to to Drummond's Bank (where his brother, Charles, was a partner). McNaughten approached Drummond from behind and shot him in the back with a ball-and-cap pistol. McNaughen was apprehended as he attempted to draw a second pistol. His statements at the time indicated that Prime Minister Robert Peel was his intended target.

At trial, counsel, Sir Alexander Cockburn, presented evidence that McNaugten suffered delusions that he was being followed by spies, persecuted by a parcel of Jesuits, and being driven into financial ruin by the Tories and Catholics. At his arraignment he said, ""The Tories in my native city have compelled me to do this. They follow me and persecute me wherever I go, and have entirely destroyed my peace of mind. They followed me to France, into Scotland; in fact, they
follow me wherever I go. I can get no rest from them night or day .... in fact, they wish to murder me. It can be proven by evidence, that's all I have to say."

A jury found him not guilty by reason of insanity, and he spent the rest of his life in the Bethlem Asylum in London. After his controversial "acquittal," the House of Lords asked a committee to research and report on the insanity defense.

For an excellent factual summary of M'Naghten, see J. Thomas Dalby, Ph.D., The Case of Daniel McNaughten: Let's Get the Story Straight, 27 Am. J. Forensic Psychiatry 17 (2006), https://www.academia.edu/25334468/The_case_of_Daniel_McNaughton_Lets_get_the_story_straight.