Took Leng How v Public Prosecutor

Took Leng How v Public Prosecutor is a landmark Court of Appeal decision arising from the widely publicized murder of Huang Na. The appellant was convicted of murder and sentenced to death; on appeal, the Court of Appeal clarified the principles governing the defence of diminished responsibility under Exception 7 to section 300 of the Penal Code and the standard of appellate review of trial judges' factual findings, particularly those resting on expert psychiatric evidence.

The appellant was convicted of the murder of an eight-year-old girl. At trial, the defence raised diminished responsibility under Exception 7 to section 300 of the Penal Code, relying on psychiatric evidence that the appellant suffered from a mental abnormality. The trial judge rejected the defence and convicted the appellant of murder.

Whether the trial judge erred in rejecting the defence of diminished responsibility, and the proper standard by which an appellate court should review a trial judge's findings of fact, especially when those findings turn on expert evidence.

The Court of Appeal dismissed the appeal and upheld the conviction for murder. The Court held that an appellate court will not ordinarily disturb a trial judge's findings of fact unless they are plainly wrong or reached against the weight of the evidence. The Court also clarified the legal test for diminished responsibility, holding that the abnormality of mind must substantially impair the accused's mental responsibility for his acts.

An appellate court will interfere with a trial judge's findings of fact only where the findings are plainly wrong or against the weight of evidence, particularly where the trial judge has had the advantage of seeing and hearing witnesses. For the defence of diminished responsibility to succeed, the accused must prove on a balance of probabilities that he was suffering from an abnormality of mind that substantially impaired his mental responsibility for the killing.

The Court of Appeal emphasized that trial judges are uniquely positioned to assess the credibility and reliability of witnesses, including expert witnesses, and that appellate intervention is warranted only where there is demonstrable error. In this case, the trial judge was entitled to prefer the prosecution's psychiatric evidence over that of the defence. The Court also elaborated on the interpretation of Exception 7, clarifying that substantial impairment requires more than a minimal or trivial effect on mental responsibility.

This case is foundational for understanding the narrow scope of appellate review of factual findings in Singapore and remains the leading authority on the legal test for diminished responsibility. It is regularly cited in both criminal appeals and cases involving the defence of diminished responsibility.

Took Leng How v Public Prosecutor [2006] 2 SLR(R) 70 (CA)