One of the first instances when the “not guilty by reason of insanity” defenses was used involved the following defendant:
Daniel M’Naughten
M’Naughten was put on trial in 1843 on charges of murder for killing the Prime Minister’s secretary Edward Drummond (it is believed that he thought Drummond was the Prime Minister). This case established the “M’Naughten Rules” in law that pertain to the insanity defense.