Just weeks after a Vietnamese woman paid Wong Jun Siang $5,000 through a middleman to get hitched to him in a sham marriage, he organised a similar hook-up for a couple, bagging $7,000 in the process.

Wong, then 22, arranged for a Vietnamese woman to marry a Singaporean man who later sponsored her Visit Pass applications to remain in the country.

The Immigration and Checkpoints Authority (ICA) uncovered Wong's web of deceit within 48 hours of his arrest in October 2014.

Assistant Superintendent Christopher Gomez, who was in the investigation team, said Wong revealed during questioning that a Vietnamese woman, Pham Thi Nga, had arranged his marriage to her sister. Nga, 31, had collaborated with another Singaporean, Chee Wee Siang, 29.

Wong, who was facing financial difficulties, took up the offer to marry Pham Thi Theu so she could remain in Singapore. They did not live together.

Armed with the information, an ICA team searched for the rest simultaneously.

In two days, they rounded up four others. Besides Vietnamese woman Le Thi Phuong, 34, and her 25-year-old husband, Benson Lim Wei Sheng, ICA officers picked up Chee and Nga.

The four were convicted and sentenced to jail terms ranging from 18 weeks to 11 months, between November 2014 and October 2015.

For arranging and entering into a marriage of convenience, as well as abetting and making false statements to get a Visit Pass, Wong, now aged 24, was sentenced to 11 months' jail.

He was convicted last December.

Wong was one of 43 people convicted over marriage-of-convenience offences last year. This figure dropped from 64 cases in 2015, according to ICA statistics released yesterday.

ASP Gomez said: "Often, during investigations, we find out that they don't live together, or consummate their marriage as husband and wife."

He said such sham marriages involved sums of up to $12,000 around four years ago, but the amount has dropped to $5,000 or so.

Staff Sergeant Jamie Tan, lead investigator for the case, said: "It involves people of all ages. If they need money, they are interested."

Seow Bei Yi