The plea of insanity in criminal cases can be traced back at least to the Babylonian Code of Hammurabi, which dates from 1755-1759 BC. It is a complicated defence, and its origins in modern law lie with the ''M''Naghten Rules'' of 1843, formulated by British judges as a jury instruction in cases where a plea of insanity had been entered. Daniel M''Naghten shot and killed one Edward Drummond, believing him to be the British Prime Minister, Sir Robert Peel, and was acquitted on the grounds of insanity, and the M''Naghten Rules still exert considerable influence over defences today. Clearly a plea of insanity in murder cases is of critical importance when the death penalty is still applied, and even today it may still be the difference between a life sentence in a high-security prison, or an indeterminate one in a secure psychiatric hospital. Meanwhile, 27 of the USA''s 50 states have retained or readopted the death penalty, and at least 54 other countries, including China, Russia, India,
