The public prosecutor will not appeal against mixed martial arts instructor Joshua Robinson's four- year jail sentence, the Attorney- General's Chambers (AGC) said yesterday.

But the AGC will discuss with the Ministry of Law whether relevant legislation should be reviewed to enhance sentencing for similar offenders in the future.

In a statement explaining its position yesterday, the AGC said that among its considerations was that securing a guilty plea from Robinson spared his three young victims "the trauma of testifying and being cross-examined at trial".

The American's sentence last Thursday sparked a strong public reaction. An online petition, started on Sunday, called the punishment "unacceptable and absolutely intolerable". It has attracted more than 27,000 signatures.

Robinson, 39, was jailed for making obscene films, having consensual sex with two 15-year-old girls and showing an obscene clip to a six- year-old girl, among other offences.

The AGC said there were calls from the public for an appeal against the sentence imposed, and for caning to be imposed. There were also public comments saying he had committed "sexual assaults" and should have been charged with rape, statutory rape or outrage of modesty.

But the AGC clarified that as the two victims were above 14 years of age when they had sex with Robinson, he had not committed statutory rape. Under the law, having sex with a minor below the age of 14 is recognised as statutory rape.

And because the girls consented to the sexual acts, he could not be charged with rape and outrage of modesty. By the same token, these were not cases of sexual assault.

Responding to suggestions that he should have been sentenced to caning, the AGC added that "caning is not provided for any of the offences Robinson was charged with". The AGC said its decision was "broadly in line with relevant sentencing precedents".

The prosecution had sought a total sentence of four to five years' imprisonment, and its position was made known to the defence counsel and District Court at a pre-trial conference last September. It was also conveyed to Robinson before he decided last December to plead guilty.

In discharging its duties, the AGC said it does not differentiate between Singaporeans and non-Singaporeans.

Home Affairs and Law Minister K. Shanmugam yesterday said "the original decision on what sentences to ask for was cleared at the highest levels - by the previous A-G himself, based on precedents from previous cases".

But he added that if there is the sense that the sentences, based on precedents, are inadequate, "we consider what can be done".

"I do think that the sentences for such offences committed by Robinson need to be relooked at," he said. "That is why I have asked my ministries to study this."

Said Association of Criminal Lawyers of Singapore president Sunil Sudheesan: "It would be unfair to level undue pressure on the prosecution or district judge, given that they are basing sentencing positions on established case law."

Compared with similar cases, he noted, four years is a long sentence.

For instance, in 2015, the jail term of a 23-year-old man was increased from four to 10 months for having sex with a 14-year-old girl whom he met via an instant messaging application.

When contacted, the six-year-old girl's father told The Straits Times that he accepts Robinson's punishment and hopes the case raises awareness of the man's conduct.

He also hopes the authorities will look into the existing system and consider having harsher punishment for similar cases.

"That's all I want, I want the Government to look into it," he said. "As for my family and I, we want closure. We are not angry. I'm content, and I want to move on."