On 15 June 2000, 65-year-old part-time taxi driver Ong Huay Dee (翁伙俤 Wēng Huŏdì)[a] was murdered by a passenger while he was driving along Pasir Ris in Singapore.

[4] Ong, who lived in Pasir Ris with his eldest son (aged 45 in 2000), was a retiree who began to work as a part-time taxi driver under NTUC Comfort (present-day ComfortDelGro) for more than a year before he was killed.

[13][14] The police found that Ong sustained a gaping wound on his head, and according to the forensic pathologist Dr Teo Eng Swee (who performed the autopsy on the victim), the various injuries on Ong's head was caused by at least four blows inflicted with a blunt object like a hammer, and he said that the injuries were sufficient to cause death in the ordinary course of nature.

Merely two months later, on 8 August 2000, 42-year-old taxi driver Koh Ngiap Yong was brutally murdered by three armed robbers at Chestnut Avenue of Bukit Batok.

[24][25] As of the time when Ong was killed, the last robbery-murder case of a taxi driver occurred in January 1995,[26] when 47-year-old taxi driver Lee Kok Yin was robbed and murdered by four Thai workers; only two of them were arrested, resulting in one sentenced to death for murder while another was sentenced to five years' jail with caning for attempted robbery.

[30] The motive of the crime was established to be robbery, since his mobile phone and wallet containing S$60 were missing, although Ong's gold chain and jade bangle were left untouched.

[16] On 29 January 2001, 26-year-old Khwan-On Natthaphon stood trial at the High Court for the murder of Ong Huay Dee in June 2000.

[49] Coincidentally, Justice Rubin was the same judge who sent three armed robbers to the gallows for murdering another taxi driver Koh Ngiap Yong, who died two months after Ong was killed.

[16] It was revealed that before he confessed, Khwan-On initially denied the killing and also tried calling his girlfriend to testify he had an alibi to the authorities when the murder occurred.

[52][53] Dr Douglas Kong Sim Guan, the defence's psychiatrist, testified on Khwan-On's behalf that he was suffering from major depressive disorder.

Dr Kong stated that based on Khwan-On's account, he had been losing concentration in his work a month before the murder of Ong, and also suffered from constant headaches and insomnia, and turned to alcohol.

Dr Tan said that the defendant did not suffer from any diminished responsibility, since he had a good work performance and got along well with his colleagues, and was able to coherently and clearly instruct the deceased victim to drive him to his destination.

He also found that Khwan-On was in full control of his mental faculties when committing the crime, and he intentionally inflicted the fatal head injuries in furtherance of his intention to commit armed robbery, such that the injuries caused were in the ordinary course of nature to cause death, and that Khwan-On never done so in a dazed and dissociative state, and fully conscious of his actions.

[60] Ong's children reportedly went to a Kong Meng San columbarium to pay respects to their father after the end of the trial.

[61] While he was held on death row at Changi Prison, Khwan-On Natthaphon filed an appeal against his sentence and conviction for murdering Ong Huay Dee.

On 19 November 2001, the Court of Appeal's three judges - Chief Justice Yong Pung How, and two Judges of Appeal L P Thean (Thean Lip Ping) and Chao Hick Tin - rejected Khwan-On's appeal,[62] affirming the original trial judge's decision to dismiss his defence of diminished responsibility, and also upheld that his claims of not having the intent to cause death or any bodily injury resulting in death should not exonerate Khwan-On from his murder charge and death sentence.

[63] After receiving word of Khwan-On's case, international human rights group Amnesty International made a public appeal to Singapore to spare Khwan-On's life and commute his death sentence to life imprisonment on the grounds that he had a mental disability at the time of the murder.