Abstract
Article 39 of the Penal Code provides a system whereby criminal responsibility may be reduced or
exempted when a specific mental disorder is recognized, on the grounds that such a disorder diminishes or
eliminates the offender’s capacity for responsibility. The nature of psychiatric evaluation in determining
criminal responsibility has long been the subject of extensive debate, with the controversy between the
“agnostic theory” and the “cognitivist theory” representing a central point of contention.
In this paper, while referring to the judgment handed down in connection with the 2023 incident in Nagano
Prefecture in which four individuals were killed, I examine what forms of psychiatric evaluation may be
conceivable in cases where the conduct in question is driven by delusional beliefs. To this end, I construct a
hypothetical case and analyze what types of evaluative methods and frameworks might be applied to such a
scenario.
Although issues such as double orientation and the essential nature of mental disorders are significant, they
fall outside the primary focus of this paper and risk rendering the discussion diffuse and overly expansive.
Therefore, these matters are reserved for future research.
