SINGAPORE - A teenager was on Monday (April 3) sentenced to reformative training for abetting another to rape a 13-year-old girl by pinning her arm.

Although Bryan Ong Jing Chong was found suitable for both probation and reformative training, the prosecution maintained its submission for a Reformative Training Centre (RTC) term for the 18-year-old.

He could spend at least 18 months and up to three years in RTC.

Ong, who pleaded guilty in February, was convicted of abetting Alson Tan Yu Seng, 18, to rape the Secondary 1 student at the latter's Bukit Panjang home some time in December 2013. Both were then 15 years old.

He had also admitted to gaming in public at a backlane in Geylang on Aug 31 last year. Two other charges of sexually penetrating the victim and attempting to rape her were taken into consideration.

The cases against two others - Tan Wei Guang, 19, and Koh Rong Guang, 24 - are pending.

Deputy Public Prosecutor Stella Tan described to the court the sequence of events that led to Ong's role in the crime.

The victim got to know Wei Guang through Facebook in 2013, and had developed feelings towards him after they began communicating on the social media site.

But towards the end of 2013, she was allegedly raped by Koh at a staircase near Yew Tee Foodfare food court. Koh was then allegedly the headman of a gang and Alson was a member of Koh's gang.

During the rape, Koh knew Alson was watching and asked if he wanted to join in, but Alson declined. Koh then threatened Alson so that he would not reveal what he had seen.

In December 2013, Ong, Alson and Wei Guang were playing basketball when the victim turned up, wanting to meet Wei Guang.

After the game, they all went to Alson's flat. He suggested they have sex with the victim. He said he had seen Koh have sex with her.

Ong and Wei Guang agreed. They let the victim go only after they heard Wei Guang's brother knock on the window of Alson's room.

On July 4, 2014, the victim reported to the police that she had been raped.

Arguing for RTC to be imposed, DPP Tan said Ong's risk of re-offending was assessed to be "moderate"; his offences were serious; and he participated willingly in both offences.

She said the victim, who is still recovering from her assault, was only 13 and defenceless against the three accused.

Defence lawyer Henry Lim, who asked that his client be given a chance, said Ong committed the offences due to peer pressure. His performance in school (Institute of Technical Education) was good, and he is motivated to do well.

Alson has been sentenced to RTC for rape and rioting.

The maximum penalty for raping a woman below 14 without her consent is 20 years' jail with at least eight strokes of the cane.