Swiss Juerg Buergin, a former UBS executive, pleaded not guilty on Tuesday to two charges of commercial sex with a minor.

The 41-year-old is the first among the 51 men charged for having paid sex with the victim, who was then 17 years old, to go on trial.

So far, 18 men have been convicted and sentenced for having paid sex with the victim.

Buergin, who has lost some weight since he first was first charged, is alleged to have paid $600 for the minor's sexual services at Shangri-La Hotel on Sept 29, 2010 and $650 at Mandarin Oriental Hotel on Jan 3, 2011.

At the start of the trial, Deputy Public Prosecutor Kavita Uthrapathy applied for the minor's evidence to be heard in camera. She said it was expedient in the interests of justice to do so, especially considering the fact that the victim was a vulnerable witness who is susceptible to mental and emotional injury.

Despite the gag order that had been issued against any publication of her name and anything that will lead to her identification, online speculation as to her identity was rife, added the DPP.

If the court rejected the application and the victim is made to testify under the glare of public scrutiny, Ms Kavita said there is nothing preventing all and sundry from attending the hearing and uploading information on the Internet, hence nullifying the gag order that is in place and fuelling even more public speculation on her identity.

Ms Kavita described the victim, who has since turned 20, as a crucial prosecution witness for the trial and potentially 30 future trials and the law must provide her with the protection she deserves for coming forward to tell her story.

Counsel Selva K. Naidu, however, objected to the application, saying the victim had received a substantial amount of money from from commercial sex and was not asked to disgorge the $21,700 she kept for herself out of $43,400.

District Judge Eddy Tham allowed the prosecution's application.