The foundation case in so far as modern insanity in the criminal law is concerned is that of Rex v. M'Naghten in 1843. In that case the defendant suffered from an insane delusion that Sir Robert Peel, a predecessor of mine in a different jurisdiction, was persecuting him and he believed that Peel had to to be killed. However, he killed Peel's unfortunate secretary by mistake. At his trial M'Naghten was acquitted because of insanity. The decision of the court caused so much public outrage that the House of Lords requested the Law Lords to explain the defence of insanity. The answer formulated by the Law Lords has come to be known as the M'Naghten Rules which have formed the basis for the development of the defence of insanity, albeit within extremely narrow limits, in the countries with common law systems ever since.