Lloyd Blankfein, chief executive of Goldman Sachs, said that a former board member at his bank had violated bank confidentiality when talking to Raj Rajaratnam, the billionaire Galleon fund manager accused of insider trading.

Prosecutors allege that Rajiv Gupta, the former Goldman Sachs board member, relayed secret information about Goldman’s earnings and investments, often just minutes after board meetings, to Mr Rajaratnam, who then traded on it. Prosecutors must convince the jury that the information was material in order to prove insider trading by Mr Rajaratnam. Asked whether the disclosure of boardroom talks would violate Goldman’s confidentiality policies, Mr Blankfein said “yes”.

Mr Blankfein was questioned about Warren Buffett’s investment of $5bn into Goldman in 2008, in the midst of the financial crisis. He said the board approved Mr Buffett’s investment during a special meeting on September 23, 2008. The decision followed Lehman Brothers’ bankruptcy and Bank of America’s purchase of Merrill Lynch over a weekend when the markets were “uncertain”.