When does the insanity defence apply? Some recent cases

This paper provides a “first principles” analysis of the role and application of the insanity defence. The defence works primarily as a mechanism for qualifying the normal rules of criminal liability as applied to mentally disordered offenders, balancing D’s individual (lack of) blameworthiness against the need for public protection. In order to perform this role effectively, we contend that the insanity defence must have an exclusionary effect. If the elements of the defence are satisfied, it should be applied at the exclusion of other overlapping (and otherwise alternative) rules. For example, where D might otherwise escape liability on the basis of lack of mens rea or via an alternative defence, if his plea is founded either directly or indirectly on a defect of reason arising from a disease of the mind, the insanity defence should be applied to the exclusion of these alternatives. Having established doctrinally this exclusionary effect in Pt 1, Pt 2 examines a number of recent cases where it has not (or has not fully) been recognised. These cases also prompt reflection in Pt 3 on which conditions should be categorised as a disease of the mind for the purposes of the insanity defence.