New York : In a development that could bolster the defence of former Indian American Goldman Sachs director Rajat Gupta, US prosecutors have started a new insider trading investigation involving a current employee of the firm.

The investigation, first disclosed in a pre-trial hearing for Gupta here Thursday is being conducted by prosecutors in the U.S. Attorney's office in Los Angeles, CNBC reported.

Gupta's trial begins May 21 on charges he provided illegal inside information to Galleon Group co-founder Raj Rajaratnam, who was convicted last year of masterminding an alleged $70 million insider trading ring and is serving an 11-year prison sentence.

Defence attorneys claim Gupta was not Rajaratnam's tipster-that another Goldman employee was, and this new disclosure could bolster that claim.

The employee, who was not identified in court, is reportedly under investigation for providing inside information about Apple and Intel.

The unnamed employee is the second Goldman Sachs person to be mentioned as an alleged tipper to Rajaratnam.

During the court hearing Thursday, Gary Naftalis, Gupta's lawyer, said he was notified late Wednesday by a prosecutor in New York that the Los Angeles office is investigating a current Goldman employee.

At a court hearing earlier this year, Naftalis said a Goldman employee allegedly passed non-public information about Apple and Intel to Rajaratnam. Neither of the Goldman employees has been accused of wrongdoing.

Gupta has denied wrongdoing. His lawyers have said he and Rajaratnam were no longer friends at the time of the alleged tips.

The lawyers have said "the wrong man is on trial", citing the other people who may have had the alleged inside information and passed it on to Rajaratnam.