While Singapore courts have been clear on when to exercise judicial mercy, there is "considerable confusion" as to the relevance of ill health in cases where judicial mercy is not justified.

Amicus Curiae Jordan Tan made this point in his report to the court at Monday's hearing.

Mr Tan had been tasked by the court to address five key issues related to judicial mercy.

His research entailed a study of the court's practice of judicial mercy and ill health in dealing with offenders in England, Australia, Hong Kong and Singapore. He suggested the court hearing Chew Soo Chun's appeal "provide guidance in the form of an overarching framework on the exercise of judicial mercy and the relevance of ill health as a mitigating factor in cases in which judicial mercy is unwarranted".

Mr Tan noted that Singapore courts exercised judicial mercy in "exceptional" circumstances, such as in the case of convicted offender Tang Wee Sung in 2008 who was suffering end-stage renal failure at the time and was sentenced to a day's jail and fined $17,000. The court found that Tang's health was likely to be aggravated by a jail term and that incarceration itself would likely have much harsher consequences for him than an ordinary offender.

Mr Tan said: "Of the 49 cases identified in which a plea for judicial mercy had been rejected, in 10 cases the courts have nonetheless given a sentencing discount but in 39 other cases the courts have rejected the plea for judicial mercy and given no discount."

Mr Tan suggested that within a general framework, where judicial mercy is not justified, an offender's ill health may nonetheless be a mitigating factor in sentence discount if it is shown the jail term would cause a greater burden on him.

He noted there is currently no single case here that provides guidelines on the interaction of judicial mercy and the reduction of jail terms based on ill health as a mitigating factor.

K.C. Vijayan