An engineer was fined $6,000 yesterday for tapping a polytechnic student on her buttock.

Wong Song Biao, 26, pleaded guilty to using criminal force to outrage the 19-year-old's modesty at the lift lobby of a block of flats in Yishun on Oct 15 last year.

The court heard that Wong was in Yishun after taking the MRT from Ang Mo Kio at about 8.30pm that day.

When he alighted from the train, he spotted the victim and found her attractive, said Deputy Public Prosecutor Kavita Uthrapathy.

He decided to follow her upon exiting the station fare gates.

At the time, the victim was on her way home. The victim, now 20, did not notice Wong tailing her.

Wong followed her all the way to the lift lobby of her block, and while she was waiting for the lift, he quickly walked up to her and used his left index finger to tap her on the buttock.

The victim was shocked and outraged by his action.

She noted that he was wearing a blue T-shirt with the words "Team ITE" in white on the back.

Wong left the scene but a police camera had caught him committing the offence.

The victim reported the matter to the police the next day.

Through follow-up investigations, police arrested Wong five days later.

District Judge Kan Shuk Weng said that having considered the facts of the case and the submissions made by the parties, she felt that the requirement for a jail sentence had not been met, and a hefty fine would be sufficient.

Wong, represented by Criminal Legal Aid Scheme advocate Sadhana Rai, could have been jailed for up to two years, fined, caned or received any combined punishment.