A former financial consultant-turned-government witness was spared prison time Thursday and given only two years of probation after prosecutors credited him with helping convict a pair of Wall Street titans on insider trading charges.

Anil Kumar had pleaded guilty in 2010 to conspiracy to commit securities fraud and other charges and agreed to cooperate in the investigation of two old friends _ disgraced hedge fund manager Raj Rajaratnam and former Goldman Sachs board member Rajat Gupta. Both were convicted at separate trials in federal court in Manhattan on charges accusing Gupta of feeding Goldman secrets to Rajaratnam.

Before hearing his sentence in federal court in Manhattan, the 53-year-old former McKinsey & Co. director told the judge that he was "completely and totally shamed" by his conduct. "I strayed from my core beliefs," he said.

Judge Denny Chin said he was swayed by prosecutors' effusive praise of Kumar as a key witness in what they have billed as the biggest hedge fund insider trading probe in history. Assistant U.S. Attorney Reed Brodksy called his cooperation "extraordinary" in part because he was forced to betray Gupta, someone he viewed as a mentor.

"He never complained about it," Brodsky said. "He provided us with full information."

At a closely watched trial last year, Kumar testified that Rajaratnam _ his former business school classmate and billionaire founder of the Galleon hedge fund firm _ broke the law by speaking regularly about the negotiations over the acquisition of ATI Technologies Inc. by Kumar's client, Advanced Micro Devices Inc., before the deal was announced.

"I told him that this was `red hot' and shouldn't be discussed," Kumar said. Later, he said, he cautioned Rajaratnam, "This is going to be a complete shock to the industry ... so treat this with the strictest of confidence."

Rajaratnam raked in $20 million by trading on the inside tip about the ATI-AMD deal. Afterward, he called Kumar at home and said, "You're a star," Kumar told the jury.

When Rajaratnam later informed Kumar that he would be rewarded with a $1 million kickback, "I almost fell off my chair," the witness said.

At Gupta's trial this year, the government used Kumar's testimony to undermine defense claims that Gupta had no financial stake in Rajaratnam's business ventures. The witness described a 2007 meeting that he had with Gupta and Rajaratnam during which they discussed starting an investment firm called Galleon Global Group.

Gupta's role would be one of "a sponsor, a wise man, a strategy person, a raiser of funds, those kinds of things," Kumar testified.

The insider trading case hinged on dozens of conversations recorded by FBI agents using court-approved wiretaps of Rajaratnam's cellphone.

In a 2008 call between Rajaratnam and Gupta, Rajaratnam described Kumar's value as someone who "is constantly ... scheming is not the right word, but constantly trying to figure what other people's angles are."

He added: "And I, you know, honestly, Rajat, I'm giving him a million dollars a year for doing literally nothing."

Responded Gupta: "I think you're being very generous."

Rajaratnam, from Sri Lanka, is serving an 11-year prison term, while Gupta, a native of Westport, Conn., is awaiting sentencing.

Kumar was also ordered to forfeit $2.26 million.