CEO Lloyd Blankfein listened as prosecutors played snippets of a 2008 telephone conversation between Galleon founder Raj Rajaratnam and ex-board Goldman member Rajat Gupta and then said that Gupta had broken the rules in the chat.
Prosecutors called Blankfein as a witness in the trial of Rajaratnam, who is accused of making more than $50 million through illegal trades by extracting secrets from other financial professionals and employees at public companies. Rajaratnam has said through his lawyer that he only traded based on information that was already known.
Prosecutors have said Gupta called Rajaratnam, founder of the Galleon funds, twice to give him tips. They said Rajaratnam then traded hundreds of thousands of shares of Goldman Sachs stock.
Gupta has not been charged criminally in what prosecutors say is the largest hedge fund insider trading case in history.
The Securities and Exchange Commission has filed civil charges against Gupta, saying he tipped Rajaratnam seven minutes before the stock markets closed on Sept. 23, 2008, causing Rajaratnam to buy $175,000 shares of Goldman stock within a minute of receiving the tip.
A prosecutor asked Blankfein about a board meeting that day, when the board approved an offer from Warren Buffett's Berkshire Hathaway to invest $5 billion in the investment giant.
Blankfein said the transaction would be received well by investors.
"However shape we were in before, they would think we were in better shape as a result of this," he said. Blankfein called Buffett a "very, very shrewd and successful investor" and said his investment would be a positive sign to the markets at a time of financial crisis.
Blankfein also testified about a board meeting on Oct. 23, 2008, when board members were told that Goldman was facing a quarterly loss for the first time since it had gone public in 1999. He said the company was "concerned that this number would be a surprise" to investors, because the consensus in published reports was that the company was making money.
The SEC has said Gupta called Rajaratnam 23 seconds after the meeting ended to reveal the expected quarterly loss, causing Rajaratnam to sell his entire position the next morning.
The trial is in its third week.
Rajaratnam, who was arrested in October 2009, is the biggest name to be charged in a probe that has resulted in more than two dozen arrests. Already, 19 of those arrested have pleaded guilty, and many of them are cooperating with prosecutors.