The Malaysian-born suspect, Ong Teng Siew (王廷守 Wáng Tíngshǒu), stated that he was suffering from intoxication of alcohol and opium and was also provoked by alleged insults from Ng leading to his homicide.

[1][2] Just four months before in August 1995, Goh Tin Luan, who posed as a government officer, had cheated Ng of S$11,000, and also targeted several other elderly victims.

[6] Dr Teo Eng Swee, the forensic pathologist, later certified that the slash wound was measured 15 cm deep and was caused by a knife, and it had cut through the gullet, several blood vessels and neck muscles, and it was sufficient in the ordinary course of nature to cause death due to it resulting in Ng dying from acute haemorrhage.

[8][9] On 29 July 1996, Ong Teng Siew stood trial for the murder of Ng Gee Seh at the High Court.

Dr Lim testified that based on the level of alcohol and opium in Ong's blood, and his account of what happened, it was plausible that Ong was suffering from diminished responsibility as induced by alcohol intoxication and effects of opium consumption, and it affected his mental faculties at the time of the offence, and also rendered him reacting vehemently to the provocation given.

However, Dr Tan Soo Teng, the prosecution's psychiatric expert, testified that Ong's mental state was not substantially impaired by the combination of drug and alcohol intoxication, and he was able to harness his self-control at the time of the offence.

In his judgement, Judicial Commissioner Singh found that Ong's mental state was not substantially impaired as a result of alcohol intoxication and the effects of opium consumption.

Based on this, Judicial Commissioner Singh decided that Ong's defences of diminished responsibility and sudden and grave provocation were ought to be rejected.

[11][7] The judge also found that Ong had not disputed the fact that he intentionally slashed the throat of Ng, such that the bodily injury inflicted was sufficient in the ordinary course of nature to cause death, and therefore his actions constituted as an act of murder under the law.

[14] In September 1996, while Ong Teng Siew was incarcerated on death row at Changi Prison and pending his appeal against his conviction and sentence, Ong suffered from a violent outbreak of a skin disease, sustaining red rashes and disfigurement on his body and face, and he was hospitalized at Changi Hospital for the disease.

[15][16][17] This disease had re-emerged following the end of the trial due to Ong's distress at the possibility of entering the gallows for murdering Ng Gee Seh.

Ong's previous suicidal tendencies in his youth and before the killing, his inability to control his temper and his hallucinations were also cited to support the defence of diminished responsibility.

He also had the opinion that Ong had murdered Ng in a moment of extreme anger and violence, and was normally bad tempered enough to even assault his wife or acquaintances on previous occasions.

[32][33] Based on this information, Wong Siew Hong argued that these instances were solid proof that Ong had indeed suffered from diminished responsibility due to the effect which Darier's disease had on his mental state of mind, and he also argued that Dr Tan's disclosure of the drug dosage could only give credence that Ong was likely behaving under the effects of the drug during the trial, which had affected his responses to cross-examination and his demeanour in court.

Arguing that his client had been "heavily doped" during his trial, Wong pointed out that this was grossly unfair to Ong because he should be in a state of mind where he required the best sense of concentration and alertness to testify and present his defence in court, especially since he faced a charge of murder that could potentially result in a death sentence, and he needed to save his life in such a situation.

The defence's psychiatrists also expressed their concerns about Dr Tan's decision to prescribe the drug as it was not meant to soothe and calm a person's mind but only to treat psychiatric illnesses, and the effects of the drug would have caused Ong to unable to maintain the best mental state to undergo a trial, even if he was assessed to be fit to plead and stand trial.

Ong's former lawyer Wong Siew Hong (aged 35 in 1998), who was a self-professed tech-savvy lawyer, stated that it was a stab in the dark when he first inquired the Internet about the nature of Darier's disease, which allowed him to obtain information that were crucial to help Ong escape the gallows for murdering Ng Gee Seh, and he also expressed his satisfaction over the outcome.

Dr Lim Yun Chin, the psychiatrist who assessed Ong, was also interviewed to speak more about Darier's disease and its implications on those diagnosed with it.