Out of curiosity, he started tailing a black multi-purpose vehicle (MPV) that kept drifting from lane to lane on the Central Expressway (CTE).
That was how interior designer Jumardi Mudah, 40, ended up witnessing a horrific tragedy in which four people were crushed to death in an accident on Aug 9, 2013.
The victims had been standing behind their Toyota Wish for a mere two to three minutes before the Honda that Mr Jumardi was tailing slammed into them.
Their injuries were so gruesome that District Judge Low Wee Ping said he was too shaken and needed more time to decide on an appropriate punishment for Toh Cheng Yang, who was driving the Honda. (See report on facing page.)
These details emerged yesterday when Toh, 36, pleaded guilty to causing death by driving in a manner dangerous to the public, and driving under the influence of drugs.
The victims were Singaporean trainee pilot Amron Ayoub, 23, his South Korean girlfriend, Miss Song Jisoo, 24, and her parents, Madam Kim Mee-Kyung , 53, and Mr Song Jungwoo, 55.
Ms Song's elder brother, Mr Song Seounghwan, escaped unscathed because he was standing beside the car at the time.
The court heard that Mr Jumardi first noticed the headlights of Toh's Honda in his rear-view mirror while travelling on the CTE in the early hours of Aug 9, 2013.
The MPV was weaving between the second and centre lanes of the five-lane expressway.
Toh was driving home to Woodlands from a pub at Amoy Street, where he had a glass of whisky with ice, said his lawyer, Mr Abdul Hamid Sultan.
Toh overtook Mr Jumardi, who was driving between 90 and 100kmh, as they passed the slip road to Ang Mo Kio Avenue 1.
As the MPV continued drifting between lanes, Mr Jumardi inferred that Toh was either drunk or sleepy, and was trying to control his car.
Curious about Toh's unsteady and erratic driving, he started following the MPV.
Mr Jumardi, who was on the extreme right lane, later caught up and drove abreast of Toh, who was on the extreme left.
He said Toh "appeared to be in a daze" despite sitting upright and looking in front.
Mr Jumardi pulled ahead but was later overtaken by Toh again.
When he saw the MPV slow down suddenly, he concluded that Toh must have braked hard to avoid crashing into a black van in front of his Honda.
As they moved towards the Yio Chu Kang exit, he noticed Toh again drifting between two of the four lanes.
Mr Jumardi spotted a vehicle parked without hazard lights on the chevron markings of the slip road to Yio Chu Kang Road.
Toh appeared to be taking the Yio Chu Kang exit but headed directly for the chevron instead and crashed head-on into the stationary Toyota Wish.
The court heard that Mr Amron was driving the South Koreans to Changi Airport when the car had a tyre puncture.
Mr Amron stopped his car and alighted with his passengers to retrieve the breakdown sign and tools to change the flat tyre.
Deputy Public Prosecutor Winston Man noted that the deceased victims were wearing bright, visible clothing at the time.
The impact of the crash sent Mr Amron's car surging right into an adjoining lane.
His car was crumpled at the rear and its roof was dented. Toh's car had a crumpled front portion, shattered windscreen and damage to its front wheels.
The Songs died instantly. Mr Amron was pronounced dead on arrival at Khoo Teck Puat Hospital (KTPH).
Toh was taken to KTPH for treatment. He complained of chest and back pain but he had no visible injuries.
He is now out on bail pending sentencing on May 29.
1 - In his car's rear-view mirror, Mr Jumardi Mudah, 40, notices Toh Cheng Yang's MPV swaying between lanes on the Central Expressway (CTE). The MPV overtakes Mr Jumardi's car as their vehicles pass the slip road to Ang Mo Kio Avenue 1.
2 - Noticing Toh's erratic driving, Mr Jumardi tails him. After Ang Mo Kio Avenue 3, he catches up with Toh while travelling at 110kmh. He then pulls away.
3 - Toh overtakes Mr Jumardi before Ang Mo Kio Avenue 5 and nearly hits a black van on the second lane of the four-lane expressway. Mr Jumardi, who is about two lamp posts behind Toh, notices the MPV slowing down suddenly before overtaking the van.
4 - As they drive towards the Yio Chu Kang exit, Mr Jumardi sees the MPV travelling between the two left-most lanes of the CTE. The MPV does not slow down before slamming into a stationary Toyota Wish on the chevron. Four people standing behind the Toyota, which had a flat tyre, are killed.
Prosecution calls for maximum jail time
The photographs of the victims' fatal injuries were so grisly that District Judge Low Wee Ping said he was too shaken to decide on the appropriate sentence for Toh Cheng Yang.
The arm of one victim was sheared off at the elbow. Others had near-amputations of their limbs.
Judge Low said he was shocked by Toh's string of drug-related antecedents.
"Suffice to say, this court has never dealt with such a horrific traffic accident involving four deaths by a traffic offender, particularly under the influence of drugs," he said.
The prosecution urged the judge to impose the maximum penalty for causing death by dangerous driving - a five-year jail term.
It is also asking for a 20-year driving ban and felt that driving under the influence of drugs warranted a jail term, but left it to the court to decide the exact term.
In his sentencing submissions, Deputy Public Prosecutor (DPP) Winston Man emphasised the need to deter hazardous driving and drug offences.
"The court cannot be seen to condone offences of the nature committed by the accused, which rouse public disquiet and compromise the safety of other road users and the public at large," he said.
DPP Man said Toh, 36, had continued to abuse prescription medicine despite his drug-related antecedents. Nitrazepam, a hypnotic drug used to treat insomnia, was found in Toh's blood sample two hours after the accident.
It was more than twice the amount needed to produce effects like drowsiness, muscle weakness and fatigue.
Citing Toh's offences of two counts each of drug possession and consumption from 2001 to 2011, Mr Man said it was clear that Toh had not learnt his lesson.
"In the present case, the accused has resorted to abusing prescription medication with tragic consequences," he added.
In mitigation, Toh's lawyer, Mr Abdul Hamid Sultan, said his client, a former logistics operations director, has a history of anxiety due to a failed marriage, work and financial issues.
Mr Hamid, who asked for a 2½-year jail term and a $3,000 fine, said Toh had tried to perform cardiopulmonary resuscitation on one of the victims instead of escaping.
On this point, DPP Man said Toh was reportedly abusive towards medical staff at the hospital, which was not how a remorseful person would behave.
He added that it was clear the injuries on the victims were too severe for anything to be done at the time.
Mr Hamid also cited contributory factors that led to the tragedy, such as the Toyota Wish being parked at the chevron instead of close to the roadside.
It is also advisable to leave the side or parking lights on at a poorly-lit road, he added.
Judge Low said the fact the Toyota Wish was parked illegally at the chevron would be taken into consideration during sentencing.
He said he was not surprised by the prosecution's call for a maximum penalty and added that he needed to hear further submissions "as to how the court should further punishment".
"Usually, the maximum sentence is reserved for the worst case. And this court hopes that it will never see (a case worse than this)," Judge Low said.
He deferred sentencing to May 29, allowing time for the prosecution to prepare a reply to Toh's mitigation.
This article was first published on May 13, 2015.
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