Which case established the complete defence of mental illness, where the jury acquitted because the accused did not appreciate the wrongness of their action due to mental illness?

Which case established the complete defence of mental illness, where the jury acquitted because the accused did not appreciate the wrongness of their action due to mental illness?

• A. Zecevic v DPP [1987]
• B. R v Porter [1936]
• C. R v Dudley and Stephens [1884]
• D. R v Lazarus [2017]

Answer: (B)

The key idea here is the insanity defence—a complete exoneration if, because of a mental illness, the accused could not understand what they were doing or that it was wrong. The landmark authority for a full acquittal on mental-illness grounds is R v Porter (1936). In that case the court affirmed that mental illness can produce a total defense: if the illness means the person did not appreciate the wrongfulness of their act, the jury may return a not guilty verdict. This aligns with the idea that the mental state at the time of the act determines criminal liability under the relevant standard (often framed by the M'Naghten rules: the person did not know the nature or quality of the act, or did not know it was wrong). The other cases cited do not establish this broad complete-defence principle: Zecevic v DPP deals with diminished responsibility (a partial rather than complete defence), Dudley and Stephens concerns necessity, and Lazarus is not the leading authority on the insanity defence.

The key idea here is the insanity defence—a complete exoneration if, because of a mental illness, the accused could not understand what they were doing or that it was wrong. The landmark authority for a full acquittal on mental-illness grounds is R v Porter (1936). In that case the court affirmed that mental illness can produce a total defense: if the illness means the person did not appreciate the wrongfulness of their act, the jury may return a not guilty verdict. This aligns with the idea that the mental state at the time of the act determines criminal liability under the relevant standard (often framed by the M'Naghten rules: the person did not know the nature or quality of the act, or did not know it was wrong). The other cases cited do not establish this broad complete-defence principle: Zecevic v DPP deals with diminished responsibility (a partial rather than complete defence), Dudley and Stephens concerns necessity, and Lazarus is not the leading authority on the insanity defence.