SINGAPORE - A part-time tutor who sometimes refers to himself as "the Bishan gay" was sentenced to 12 months' jail on Friday for molesting a 12-year-old boy in a mall toilet.

Cheng Hoe Huat was found guilty after a two-day trial of touching the student's private parts in the male toilet of Bishan Junction 8 shopping centre on Nov 13, 2013.

The 52-year-old, who was unrepresented, is appealing. Bail of $30,000 was allowed.

During the trial, the prosecution called 13 witnesses, including the victim, his four friends, a child psychologist and teacher.

Cheng had approached a group of boys, including the victim, to "conduct a survey on sex education".

The victim accompanied him to the toilet as he thought Cheng, who was using a walking stick, needed help.

Deputy Public Prosecutor Amanda Chong argued that the victim was an "unusually convincing witness". The only discrepancy was in his memory of the exact toilet cubicle where the incident happened.

She said Cheng's defence was unsupported by any corroboration.

District Judge Lee Poh Choo said that although the CCTV footage from the mall was not clear, images of the victim and Cheng walking together could be made out.

Although Cheng denied knowing the victim and his friends, the judge said the boys, who were then 11 or 12, had positively identified him as the "old man" or "old uncle" who befriended them at Bishan Junction 8 and molested the victim.

"These are young and resourceful boys as together, they secretly videoed the accused. This video clip was important evidence establishing the accused's presence at the location on that day," she said.

Judge Lee said she found that the four boys had been "honest and frank", and did not embellish their evidence.

She agreed with the DPP that they had no motive to lie against Cheng, and convicted him of the charge.

The maximum penalty for molesting any person under 14 years old is five years' jail, fine and caning.