Student sentenced over child sex material

An international masters student who thought he was having a sexual relationship with an adult would climb into a 15-year-old girl's bedroom through her window while her family slept.

Amarashinghe Amarashinghe, 26, was acquitted by a jury earlier this year of a string of child sex charges, on the basis he honestly believed his lover was of legal age.

On Wednesday in the Victorian County Court, the Sri Lankan citizen was given a six-month good behaviour bond for one remaining charge of possessing child sex material - explicit images and videos of the girl on his phone - for which he had pleaded guilty.

"Your behaviour was most likely just foolishness rather than anything more sinister," Judge Howard Mason said.

Amarashinghe, who is in immigration detention, had met the girl on the free online dating site, OkCupid.

He was 24 and studying a masters degree at Melbourne's RMIT University.

The victim had written on her OkCupid profile that she was 21 and maintained the lie until their second or third late-night rendezvous.

They began communicating via Skype where the girl freely discussed "erotic matters", Judge Mason said.

At her invitation, Amarashinghe went to her home, entering through her bedroom window, which she had left open for him.

Once meeting her, Amarashinghe believed she was between 18 and 20, the court heard.

They met five times over a two-month period to have sex.

The victim was "a very willing partner", Judge Howard said.

Despite that, children lack the maturity that would prevent them from such behaviour at an older age and need protecting regardless of consent, the judge said.

As well as being acquitted at trial, the judge said Amarashinghe had no criminal history, had cooperated well with police and had pleaded guilty to the child porn charge.

"It is highly unlikely you would ever reoffend in this way again," he said.

Amarashinghe received a six-month order to be of good behaviour and must report to the sexual offenders' register for eight years.

Amarashinghe remains in immigration detention and it is unknown when he will be released or what his residency status in Australia will be.