New York : A superseding indictment against ex-Goldman Sachs director Rajat Gupta, an accused in insider trading scam, is expected to be filed today , according to US prosecutors, who said his "close friend" and top Berkshire Hathaway executive Ajit Jain could be a potential witness in the trial slated for April. At a hearing held in a Manhattan court , Assistant US Attorney Reed Brodsky said the deadline for the government to file the superseding indictment, which may contain expanded charges, is January 31.

US Judge Jed Rakoff said an arraignment, if the superseding indictment is filed, may take place on February 6 or 7.

The government had earlier this month said "more likely than not there will be a superseding indictment." Gupta, 63, who has pleaded not guilty to the insider trading charges filed against him last October, was not present for the hearing which lasted nearly two hours.

Prosecutors claim Gupta passed on insider information to Sri Lankan hedge fund manager Raj Rajaratnam about a USD five billion investment proposed by Berkshire in Goldman Sachs.

Brodsky told judge Rakoff that Jain could be called in as a potential witness for Gupta during the trial, slated to begin April 9.

Jain is head of Berkshire Hathaway's reinsurance business and has been touted as a possible successor to company CEO Warren Buffet. Jain had been interviewed by Gupta's defence team before he met the prosecutors.

"Ajit Jain, a close friend of Gupta's, spoke to us after he spoke to the defence. My understanding is that he spoke to the defence again after he spoke to us," Brodsky said. Goldman Sachs Director Claes Dahlback could also be a potential defence witness, Brodsky said.