WHEN Australian authorities deported a Sri Lankan student earlier this year, they expected he would be home soon after boarding a connecting flight in Singapore. Instead, he has vanished.

The strange case of the missing student began on February 15, when immigration officers put Sri Lankan national Randika Mallawaarchchi on a flight from Adelaide. Mr Mallawaarchchi, 24, was deported for overstaying his visa by two months.

The Singapore government has confirmed he arrived at the city-state's Changi Airport and says he boarded a Colombo-bound flight at 9.40pm on February 15.

But he has not been seen since. It is difficult to disappear mid-flight, so the options seem limited: either he is still in Singapore - or he vanished from Colombo Airport on arrival, and it is being covered up.

If Mr Mallawaarchchi arrived in Colombo he would not be the first person to disappear there.

His Canberra-based lawyer, Chanaka Bandarage, says the missing man's parents ''are in agony'' because they don't know what has happened to him.

But former housemate Kasun Perera has found a bank statement showing $200 was withdrawn from Mr Mallawaarchchi's account in Singapore on March 3 - 16 days after the Colombo flight left.

''I believe he is still in Singapore,'' Mr Perera said. ''He was a kind of mysterious character. He [was] quiet and got good grades. He kept his privacy.''

But Mr Bandarage said he did not doubt the Singaporean government.

''They said he departed from Singapore and provided a lot of detail. It is a very strange situation that the Australian Immigration Department has completely washed their hands of.''