A recalcitrant molester with degrees in economics and psychology, as well as law, was sentenced to six years' corrective training after molesting two young boys.

Since 2004, Yeo Wu Kok has been jailed twice for sexual assaults against adolescent boys.

On July 8, 2015, the 54-year-old committed his ninth offence.

While at Woodlands Bus Interchange, he found himself attracted to a 14-year-old student's "white shoes and socks". The unemployed man boarded the same bus as the student in his school uniform.

Yeo later alighted at the same bus stop in Petir Road as the boy. He lied that he was doing a photography project and asked the boy to take him to the nearest community club (CC).

After stopping at Bukit Panjang CC, Yeo and the boy walked to Senja-Cashew CC as Yeo had asked if there were any other CCs in the area.

Yeo then asked the boy to lead him to a nearby multi-storey carpark, where he massaged the boy's facial area.

Deputy Public Prosecutor Jesintha Veijayaratnam said Yeo's motive was to take photos of the boy's naked body.

He then had the boy take him to a quieter spot at the staircase landing of a block in Petir Road. There, Yeo removed the boy's socks and shoes, and molested him, said DPP Jesintha. He also took four photos of the boy, which he later deleted. He gave the boy $18 to keep mum.

Three weeks before he was to go on trial for that crime, Yeo re-offended. On June 17 last year, he approached another 14-year-old boy, who accompanied him to Woodlands CC.

After taking a photo of the victim at the CC, he led the boy to Admiralty Park and touched his lower abdominal area, before massaging his temple and eye area. The boy felt uncomfortable and Yeo offered him $50 as a token of appreciation, but the boy did not take the money. Yeo then offered him $5.

DPP Jesintha said that while they were walking in Woodlands Avenue 9, Yeo suddenly hugged the victim, who tried to push him away.

Yeo has been diagnosed with hebephilia - a strong, persistent sexual interest by adults in pubescent children aged between 12 and 14 - and bipolar affective disorder by a psychiatrist at the Institute of Mental Health.

He admitted in his police statement that after his release from prison in April 2011, he performed similar sexual acts on four other boys before the 2015 offence.

The DPP asked for preventive detention to be imposed on the "systematic sexual predator" and "menace to society".

"All the accused's past sexual encounters involved adolescent boys between the ages of 12 and 14, wherein the accused had touched his young victims inappropriately in areas, including their genitalia, and photographed them," she said.

Yeo's pro-bono lawyer Ariel Lim Huimin said her client, who has multiple degrees from Britain and Canada, was molested when he was 13 and developed a sexual attraction for young males wearing white shoes and socks. He has a family and personal history of psychiatric illnesses, she added.

District Judge Carol Ling sentenced Yeo to six years' corrective training, a strict regime for repeat offenders with no remission for good behaviour, on three charges of molestation that he admitted to.