The Japanese M’Naghten Rule: the assessment of the insanity defence in Japan

Abstract

ABSTRACT The assessment of the insanity defence for mentally disordered offenders is a significant issue in murder trials in Japan. While acts of insanity are not punishable in theory, insanity is not an absolute defence even when proven; that is, the existence of a mental disorder that influenced the crime does not guarantee that an offender will not face the death penalty. Decisions about the sanity and responsibility of mentally disordered offenders are often made without evident basis, and the lack of guidelines in this regard often leads to subjective assessments. This article provides an overview of the problems surrounding the assessment of the insanity defence, mainly the psychiatric evaluations and the wrongness limb of the M’Naghten Rules as applied in Japan. Supplemented by case examples to illustrate the inconsistencies in the decision-making process, this article highlights the need for greater clarity and consistency in the assessment of the insanity defence.