He claims he doesn't believe in the supernatural, but till this day, there remain things, or sightings, he can't explain.
Forty-year-old Desmond Wong, a member of the Singapore Paranormal Investigators (SPI), was only 16 when he met the "shadowman" in school.
It was about 3am at night, he recalled. Wong was at an overnight school camp and, try as he might, he couldn't sleep a wink.
Armed with a torchlight, the adventurous student decided to get out of bed to roam the school.
"That was the first time I met the shadowman," said Wong, who had initially mistaken the dark figure for a human being.
"It appeared along the corridor of the science block in school. I was at the other building, looking across," he added.
Curiosity soon got the better of his fear. Wong whipped out his torchlight and shone towards the ambiguity.
He was surprised to see it move.
"I think I wasn't expecting it to, but it moved. The shadowman disappeared right through the wall," he said.
"I felt a chill run down my spine," Wong recalled. "What was that?"
Over the years, Wong claimed he'd met a few more shadowmen, although he could never be sure if they were the same "person".
It happened again in 2005, this time at the infamous "Suicide Tower", an observation tower at the Pasir Ris Park's mangrove swamp where a person was rumoured to have jumped to his death many years ago.
Out on a "ghost hunt" at Pasir Ris Park, where he and his friends had booked a chalet close by, Wong and his companion soon found themselves climbing the steps of the much-talked-about tower.
"My friend and I went up and then I saw it again — the shadowman. It walked past us very quickly just as a sudden gust of wind hit us," he recalled.
Wong's spooky tale, complete with photographs and recordings, will be featured in an upcoming episodic documentary series "My Ghost Story Asia", which retells eyewitnesses' accounts of their encounters with the supernatural at reportedly haunted locations in Singapore and Malaysia.
'We're no ghost-busters'
Wong, an enrichment trainer by day, joined the SPI in 2006 because he "wanted to find out more about the paranormal world".
Founded in 2001, the SPI is Singapore's first and original paranormal group, Wong claimed.
He said that the 20-member strong group makes it a point to meet at least once a month. Equipped with high-definition night vision cameras, digital audio recorders and other high-tech gear, they would attempt to "capture" unexplained phenomena as they explored places like nature reserves and haunted buildings.
"There were times when all our equipments, including our handphones went down at the same time when no doubt, they were fully charged," said Wong, whose team had visited abandoned blocks like the Old Changi Hospital and the old Commando camps. "Things like these happen many times."
Wong added, "Sometimes, one or two members will say they hear voices, see images and even feel pokes into their backs… and most of the times, we'd hear panting noises in the recordings."
But despite all that he and his team had experienced over the years, Wong insists he doesn't believe in the supernatural.
"I'm a non-believer," he said. "I like to find out things to explain things."
"People perceive us as ghost-busters but we don't going around catching ghosts in public. We investigate so that we can explain things using scientific methods — physics, temperature, electromagnetic field factors… all of these can affect your way of thinking, your way of seeing and hearing things."
"It's hard to believe sometimes but mostly, these phenomenons can be explained," Wong added.
"People think we're very superstitious or illogical, but we're just trying to do as much as we can to gather and collect data," he said.
"And in terms of whether there is or there isn't… the evidence is there — you decide for yourself."
Do you have your own spooky tale to share? Write in to the producers of My Ghost Story Asia to have your paranormal experience featured in the next season. Visit biochannelasia.com/myghoststoryasia for more information.
My Ghost Story Asia premieres 16 August, every Thursday at 10pm on The Biography Channel (StarHub TV Ch 404).