A former full-time national serviceman with the Singapore Police Force, who preyed on underage girls online before pestering them for naked pictures of themselves, was sentenced yesterday to two years' jail.

A.R. Arun Prashanth, now 25, committed sexual acts on three of his five victims, who were then aged 12 to 15. He was also found to have snapped more than 700 upskirt photographs of unknown women with his mobile phone.

On July 31, Arun, who is now jobless, pleaded guilty to one count each of sexually penetrating a minor, performing an obscene act on her and procuring the commission of an obscene act by another underage girl.

He also admitted to four counts of insulting a woman's modesty.

The seven charges involved two minors and four unknown women.

Twenty-one other charges for similar offences, involving three other young girls and several unknown women, were considered during sentencing. The victims cannot be named because of a gag order.

Some time between February and March 2016, Arun sent a message to a 12-year-old girl through Instagram and they exchanged mobile phone numbers when she responded in April that year.

He started sending her lewd messages several times a day soon after. He also told the girl on at least two occasions that he was a policeman.

Deputy Public Prosecutor Kwang Jia Min said: "The accused pestered her for naked pictures or videos of herself showering... (The girl) felt harassed by the accused and she would try to ignore him."

The girl relented on May 8, 2016, after he repeatedly asked her for sexy photos and she sent him a picture of herself in her underwear.

Arun got to know another girl through a WhatsApp group chat in 2016 and messaged her separately. He told the 14-year-old that he was from the Home Team and she told him her age when he asked for it.

On Feb 3, 2017, she sent Arun a text message, telling him that she would be playing truant, and he invited her to his house in Hume Avenue, near Upper Bukit Timah Road.

When she arrived, he took her to his bedroom and performed an obscene act on her. He also sexually penetrated her. She later left his apartment in a private-hire car.

The court heard that the driver noticed the teenager was trembling and asked her what had happened. She told him about her ordeal and he drove her to Sembawang Neighbourhood Police Centre to lodge a report.

Officers arrested Arun at his home the next day and they uncovered 720 upskirt photos on his mobile phone during investigation.