He drugged 13 boys over a span of three years on the pretext of conducting an experiment for a school project.
Even after Sean Chew Jun Yang, 26, was first arrested in June 2012 and later released on bail, he continued to poison boys with large amounts of laxatives.
He did this because he wanted to watch his 12- to 14-year-old victims vomiting and experiencing bouts of diarrhoea.
He would also ask them to send him photographs or video clips of their vomitus and faeces.
Chew admitted deriving sexual gratification from thinking about young boys defecating and watching the images sent to him by his victims.
Yesterday, Chew, a final-year chemical engineering polytechnic student, was sentenced to a total of 36 months' jail for causing hurt and trying to cause hurt by poison.
Before sentencing him, District Judge Liew Thiam Leng said the offences Chew had repeatedly committed were "serious in nature". He also noted that Chew "had taken great pains to hide his identity".
The offences were committed between May 2012 and June 2015. None of the victims was paid.
Deputy Public Prosecutor Andre Chong said that while similar photos and videos of vomitus and faeces were available online, Chew wanted something different and decided to obtain "live" photos and videos.
The court previously heard that Chew had befriended his victims on Facebook by impersonating the students' friends or saying he was a former student from the same school.
After gaining their trust, he would tell them he was conducting an experiment and give them pills to consume so he could test their effects on hormones.
OBTAIN "LIVE" IMAGES
Chew was careful not to reveal his identity.
He left the pills at pre-arranged spots - near staircase landings and public phone booths - close to the boys' homes.
The court heard that in June 2014, a 14-year-old boy received 10 Dulcolax laxative pills from Chew, who had posed as a friend's "cousin".
The pair communicated via Skype. Chew hid his identity by covering his webcam with masking tape, claiming his webcam was spoilt.
He then instructed the boy to consume all the 10 pills at once. Six hours later, the boy had a stomach ache.
Chew told the boy to go to the toilet and record a video clip of himself defecating as he wanted to study the boy's stool. The boy obliged and later sent Chew a video clip via Skype.
The next day, Chew gave the boy another 20 Dulcolax pills.
Again via Skype, Chew told the boy to consume the pills.
The boy swallowed all 20 and had diarrhoea several hours later.
Three months later, Chew was exposed when the boy told his teacher about Chew's experiments.
This led to Chew's second arrest in September 2014. The police then found 24 pictures of faeces and 26 video clips of victims vomiting and defecating in a laptop.
Chew was arrested for the third time in July 2015 after one victim's parents made a police report in June.
Between his first arrest in June 2012 and his most recent arrest in July this year, Chew had continued to re-offend even while on bail.
The prosecution argued that Chew's persistent actions showed a complete lack of remorse and regard for the boys' safety as they were given "five to 10 times the recommended dosage".
He had selfishly and callously harmed the victims for his own sexual enjoyment.
Defence lawyer Sunil Sudheesan said it was unfortunate his client was initially not diagnosed with a fetishistic disorder.
In June 2012, after his first arrest, Chew was diagnosed with mild depression, or what is known as dysthymia.
It was only in February 2014 that he was diagnosed with a fetishistic disorder.
Mr Sunil said: "Our client's disorder was therefore left unidentified and untreated until February 2014...Our client's re-offending behaviour must therefore be viewed against this context."
Mr Sunil added that Chew remains ashamed of his actions and is committed to have his illness treated. The defence has filed an appeal against the sentence.
Chew is out on $20,000 bail.
If ignored, fetish can get out of control
Ignoring a fetish could bring peril to a sufferer.
This is the view of psychiatrist Munidasa Winslow who said that Sean Chew Jun Yang's fetishistic disorder - where he derived sexual pleasure watching boys vomiting and defecating - was no different from other forms of reported fetishes.
Dr Winslow told The New Paper: "Unfortunately, some believe they don't have a problem when they choose to ignore the problem in the first place."
If left unattended, the fetish or compulsion may get out of control.
Even the threat of being caught and punished by the authorities may not deter sufferers from realising their fetishes, he said.
The only way forward is to go for therapy, understand the disorder and learn what drives it.
But why had Chew's victims easily given in to his perverted demands even when it caused them physical discomfort?
One expert's view is that the children's innocence and gullibility made them easy targets for Chew on social media.
Dr Carol Balhetchet, a clinical psychologist and senior director for youth services at the Singapore Children's Society, said: "To the 12-to-14 age group, social media is their universe. They live and breathe it and want to believe that what's out there (on social media) is the truth. This makes them gullible and vulnerable."
Chew's victims may have also participated in the "experiments" because they felt "special" for being chosen, she added.
In 2011, a 31-year-old sales representative who claimed to have fantasies about eating children's faeces admitted to trespassing.
He had entered two kindergartens, defaced the walls of a toilet and written obscene messages on a whiteboard in a classroom.
In one of the instances, he went into a childcare centre and found several soiled diapers in a toilet. He had wanted to use them to help him fantasise while masturbating.
He ended up taking the diapers and smearing their contents on the centre's walls.
The man was arrested and sentenced to six months' jail and fined $2,500.
In 2011, a 48-year-old who derived sexual pleasure from riding motorbikes belonging to others was caught stealing an $8,700 bike at Marina Bay Sands.
He had been diagnosed with the fetish more than 20 years earlier and it had landed him in jail at least three times.
A psychiatrist found that he was suffering from depression and paraphilia, a condition characterised by abnormal sexual desires involving dangerous activities.
In 2013, a serial thief with a fetish for sniffing women's leather wallets was jailed 13 months. The 48-year-old man would get sexually aroused by the smell of leather.
He would also take upskirt pictures.
Since 1986, he had been in and out of jail. He was spared from jail in May 2011 when he was placed on probation due to his psychiatric disorder. But he repeatedly breached the order by stealing again and insulting a woman's modesty.
This article was first published on November 14, 2015.
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