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This brief essay, written for the Criminal Law Conversations Project, examines whether one can justifiably kill a faultless, insane assailant to save oneself or another from imminent and serious harm. Although scholars on both sides of the Atlantic agree that the person attacked should not be punished for defending herself from the psychotic aggressor, there is significant disagreement with regards to whether the defensive response should be considered justified or merely excused. Furthermore, amongst those who argue that the appropriate defense in such cases is a justification, there is disagreement regarding whether the specific ground of acquittal should be self-defense or necessity.

These issues are explored in three parts. Part I discusses the facts that give rise to the problem of the psychotic aggressor and summarizes the basic questions posed by the case. Part II surveys and rejects five theories that would lead to acquitting the victim of the attack if he were tried for killing the psychotic aggressor. Part III advances an autonomy-based conception of self-defense that would justify the victim's use of force against the insane assailant and would allow third-party intervention in favor of the defending party. According to this theory, the roots of the right to use defensive force are not in the culpability of the aggressor, but in the wrongful invasion of the autonomy of the defender. Given that the psychotic assailant's attack amounts to an unjustifiable attack on the victim's autonomy, the victim's reciprocal obligation to show consideration for the psychotic aggressor's autonomy weakens. As a result, the law affords him a right to use whatever force is necessary to repel the unlawful attack. The fact that the psychotic actor would be acquitted on grounds of insanity if he were tried for his aggression is beside the point, for excuses such as insanity do not negate the wrongfulness of the act. Our right to be free from unlawful interferences with our person should not be compromised merely because the threat to our autonomy originates in the acts of an inculpable person. In such a confrontation on the street, the aggressor loses the protections that he would get during a trial, that is, the right to plead excuses such as insanity or duress.


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