A former Goldman Sachs board member fed secrets about the banking giant to a close friend and fellow Wall Street heavyweight who used the information to make a killing on the stock market, a prosecutor said Wednesday in closing arguments at the board member's insider trading trial.

Rajat Gupta "abused his position as a corporate insider," Assistant U.S. Attorney Richard Tarlowe said in federal court in Manhattan.

"Gupta violated his duty to keep that information confidential by giving that information to Raj Rajaratnam," the disgraced founder of the $7 billion US Galleon hedge fund.

In his closing argument, defense attorney Gary P. Naftalis sought to convince the jury that there was "zero" evidence that Gupta profited from his own illegal trades or from kickbacks off trades by others — "the stuff a real insider trading case is all about."

The government relied on wiretaps in its 2011 prosecution of Rajaratnam and more than two dozen others in a wide-ranging probe of the hedge fund industry. U.S. Attorney Preet Bharara has billed it as the most extensive use of wiretaps ever in an insider trading investigation.

But despite making months of recordings of Rajaratnam's phone calls, none ever captured him talking about specific trades with Gupta, Naftalis said.

"You'll find there were no such conversations, because they didn't happen," the lawyer said.

The jury is to begin deliberating Thursday.

1 trade earned $1M US

During the trial that began on May 20, the government highlighted a Sept. 23, 2008, phone call it said was made from Gupta to Rajaratnam.

The call came only minutes after Gupta had learned during a confidential conference call about how Warren Buffett's Berkshire Hathaway planned to invest $5 billion in Goldman — a blockbuster deal that wouldn't be announced until the stock market closed at 4 p.m.

"That news was going to be very good news for Goldman Sachs," Tarlowe said Wednesday. "The average ordinary investor had no way of knowing that. ... Until the announcement, it was confidential."

Records show that moments after the phone call ended at 3:55 p.m., Rajaratnam purchased $40 million in Goldman stock — a trade that ended up making him nearly $1 million.

The hedge fund manager's assistant, Caryn Eisenberg, testified at trial that it was the only call her boss received on his private line that day between 3 p.m. and 4 p.m.

"That evidence is devastating for the defendant. ... If you believe Ms. Eisenberg, it's over — the defendant is guilty," Tarlowe said.

Also played at trial was a wiretap of a July 2008 phone call during which Rajaratnam grilled Gupta about whether the Goldman Sachs board had discussed acquiring a struggling bank, like Wachovia, or an insurance company.

"Have you heard anything along that line?" Rajaratnam asked Gupta.

"Yeah," Gupta responded. "This was a big discussion at the board meeting."

Both men where sophisticated enough to know it was wrong to discuss board business, yet Gupta casually spilled secrets "as if he was talking about what happened at a Yankee game yesterday," Tarlowe said.

Rajaratnam serving 11-year sentence

The prosecutor argued that Gupta was motivated to help Rajaratnam because he had a financial stake in some of the hedge fund manager's business ventures. "What was good for Raj Rajaratnam was good for Mr. Gupta," he said.

Naftalis countered that most the evidence was specific to the "secret world" of Rajaratnam and not about Gupta.

"I sometimes wondered whether Raj Rajaratnam was the man on trial," he said. His client, he added, is a victim of "pure guilt by association."

In a rebuttal argument at the end of the day, Assistant U.S. Attorney Reed Brodsky drew attention to another Rajaratnam phone call in 2008 when he told one of his traders that he had got a tip "from someone who's on the board of Goldman Sachs" that Goldman was facing an unexpected quarterly loss.

The prosecutor argued the sequence of events — the phone calls, the subsequent trades and Rajaratnam's blabbing about it — could not be dismissed as mere coincidence.

To accept the defense case, "You'd have to believe that Mr. Gupta is one of the unluckiest men in the world," Brodsky said.

Gupta, 63, was an orphaned teenager in India before gaining prominence in corporate America.

The Harvard-educated defendant is the former chief of McKinsey & Co., a highly regarded global consulting firm that zealously guards its reputation for discretion and integrity.

He had led a "busy and admirable life" before being charged with conspiracy to commit securities fraud and securities fraud, his lawyer said.

Rajaratnam is serving an 11-year prison sentence after being convicted last year on insider trading charges.