R v Fang (No. 1)

The case before the court was a murder trial where the accused relied on a partial defence of substantial impairment by abnormality of mind. The defendant, Fang, was charged with murder but claimed a diminished responsibility due to a mental condition. The court needed to determine the admissibility and weight of forensic psychiatric evidence in establishing the defence. The primary legal issues were whether the medical opinion on the degree of impairment and its substantiality was permissible and whether the court could consider the evidence in determining the degree of impairment. Additionally, the court needed to decide if the question of whether the impairment was so substantial as to reduce the liability for murder to manslaughter was a matter for the jury or the court.

The court considered the statutory framework provided by section 23A of the Crimes Act 1900, which delineates permissible areas of opinion evidence for forensic psychiatrists. It concluded that while medical opinion on the degree of impairment and its substantiality was permissible, opinions on matters listed in section 23A(1)(b) were not. The court found that the medical evidence could assist the jury in determining the extent of the impairment, but the ultimate question of whether the impairment was so substantial as to warrant a reduction in liability from murder to manslaughter remained for the jury. The court emphasised that the jury was to assess the evidence and decide whether the accused's mental condition substantially impaired their responsibility for the crime.

Ultimately, the court held that the forensic psychiatrist's evidence was admissible to the extent it addressed the degree of impairment and its substantiality. The court directed the jury to consider this evidence in determining whether the accused's mental condition substantially impaired their responsibility for the crime. However, the decision on whether this impairment warranted a reduction in liability from murder to manslaughter remained within the purview of the jury. The court provided clear guidance to the jury on how to assess the medical evidence and apply it to the legal criteria set out in the Crimes Act 1900.