SINGAPORE - A 31-year-old unemployed man was sentenced to 15 weeks' jail on Monday, for having sex with an underage prostitute.

Leu Xing-Long is the 39th man to be dealt with in connection with this online vice ring, out of the 51 men taken to court in 2012.

The former project engineer paid the then 17-year-old $450 for sex at Hotel 81 Bencoolen on 30 Sep, 2010.

Now 21, the girl was an escort listed on a website operated by her pimp.

Leu fought one charge, claiming he had been conscientious about not breaking the law and ensuring she was above 18.

But, convicting him on May 5 after a six-day trial, District Judge Ronald Gwee said there was no evidence of this in some 800 messages the man had exchanged with the girl's pimp, Tang Boon Thiew. "The messages showed instead, that his concern was mainly over which girl was available, at what price, and over details such as where and when to obtain the sexual service," the judge said.

Leu is the seventh person to be convicted after claiming trial. Five others before him have received jail terms of between four and five months, and a sixth, an 18-month probation term. The maximum penalty for the offence is a seven-year jail term and a fine.