First, he instructed a Secondary 4 boy to perform sex acts with an 18-year-old girl as he clicked away with his camera.
Then the man took off his clothes and joined them.
As the trio engaged in various sex acts, the camera, which was set on timer, continued taking photographs of them every few seconds.
The pictures were later leaked on the Internet, prompting the boy's school and his guardian's son to make a police report against the man.
Yesterday, the 41-year-old Singapore permanent resident became the first person to plead guilty here for causing the boy, who was a 15-year-old minor at the time of the incident in 2012, to have sex with a girl.
All three cannot be named to protect the minor's identity.
The man, a former IT specialist from India whom we are calling Andrew, was a photography enthusiast who engaged in nude and erotic shoots with models he found online, court papers said.
That was how he got to know the girl, whom we are calling Jennifer. She was an 18-year-old part-time model who charged at least $250 for an erotic photoshoot.
Andrew had used her previously for photoshoots before he posted an advertisement online that stated: "Hoping to fulfil my girlfriend's fantasies; seeking an extra man."
That listing on a forum drew the attention and curiosity of the boy, who was then a virgin.
He contacted Andrew, told him that he was 18 and agreed to help Andrew's "girlfriend" fulfil her "fantasies".
Sometime between October and November 2012, the three of them met in the lobby of a hotel near City Hall before proceeding to a room that Andrew had booked.
In the room, the boy told Jennifer that he was a first-year polytechnic student.
Andrew introduced himself as a Singaporean businessman dealing with Korean beauty products and an avid photographer, the boy said.
After 20 minutes of chit-chatting, Andrew set up his camera equipment and told Jennifer and the boy to pose by the sofa.
He instructed Jennifer to undress the boy, who felt uneasy but kept mum about his discomfort. Andrew assured him that the photographs were meant only for personal use.
He told Jennifer to take off her clothes then instructed her and the boy to perform various sex acts while he photographed them.
At some point, Andrew set his camera on timer mode. He removed his own clothes and joined the two on the bed.
He handed the boy a packet of condoms and told him to have protected sex with Jennifer. Andrew also had sex with her.
Afterwards, Andrew paid Jennifer $250 and they left the hotel.
In January last year, a friend of the boy saw pictures of the session and sent a text message to the son of the boy's guardian.
When the guardian's son confronted the boy, the latter was shocked and scared that the photographs were on the Internet. He admitted that it was him in the pictures. The victim's form teacher also found out about the pictures.
On Jan 9, the boy, accompanied by his guardian's son, his teacher and a school counsellor, made a police report.
The police were unable to ascertain how the photographs ended up online, court papers said.
Two other charges against Andrew will be taken into consideration when he is sentenced on March 10.