It is one of the biggest mysteries on Wall Street: Who is Tipper X, the secret witness at the center of the biggest insider-trading case in a generation?   The answer is Thomas Hardin — a young investment analyst who, the authorities claim, traded on inside information and may now lead prosecutors to other crucial players in the sprawling investigation into the billionaire Raj Rajaratnam and his hedge fund, the Galleon Group.

Mr. Hardin, 32, is one of three people named on a list of potential witnesses that the Securities and Exchange Commission recently provided to Mr. Rajaratnam and other defendants, according to people close to the case. The other two named were Ian P. Murray, a hedge fund manager in New York who has not been charged with wrongdoing, and Gustavo D’Souza, whose business affiliation and connection to the case, if any, were not immediately clear.

The link to Mr. Hardin and Mr. Murray is the latest twist in the snaking Galleon case, which has stretched from Wall Street to Silicon Valley and ensnared executives at some of the nation’s largest technology companies. Mr. Murray, a protégé of Julian Robertson, one of the titans of the hedge fund industry, runs Lanexa Global Management, where, until recently, Mr. Hardin was a managing director.

Mr. Hardin and Mr. Murray did not respond to telephone calls and e-mail messages on Tuesday. A spokesman for the S.E.C. declined to comment.

According to the S.E.C., Mr. Hardin traded on confidential information while at Lanexa and passed information to another figure in the Galleon case, Gautham Shankar, a former trader at the Schottenfeld Group.

Mr. Hardin’s supposedly illicit trades involved the pending takeover of Hilton Hotels and Kronos Inc., a software company in Massachusetts, according to the S.E.C. Mr. Shankar, whom the authorities characterize as a friend of Mr. Hardin’s, later admitted trading on inside information about that deal.

“In 2007 I got the ideas to buy Hilton and Kronos from a person who now I understand and I believe to know had inside information, and so I traded those two stocks,” Mr. Shankar told United States Magistrate Judge Gabriel W. Gorenstein in October.

According to prosecutors, Mr. Hardin is also a friend of Roomy Khan, the former Intel Corporation executive who pleaded guilty to charges of passing corporate secrets to Mr. Rajaratnam and others and is now one of the government’s star witnesses in the case. He was also used to funnel cash payments from Ms. Kahn to other sources of inside information, prosecutors said.

Mr. Shankar, 35, has been characterized by the authorities as a major link in the chain of inside information that eventually was passed on to traders at the Schottenfeld Group, including Zvi Goffer, a former Galleon employee who sought tips and paid for them, according to prosecutors. Mr. Goffer, who was nicknamed Octopussy for his vast connections to information, has denied the charges against him, as has Mr. Rajaratnam.

In February, Mr. Goffer and another defendant in the case, David Plate, apparently began worrying that Mr. Shankar was working with investigators. According to a transcript of a recorded conversation between the men, Mr. Plate and Mr. Goffer were overheard discussing the possibility that Mr. Shankar was a “rat.”

Like many of the people embroiled in this case, Mr. Hardin does not fit the stereotype of a Wall Street gunslinger. A graduate of the Wharton School at the University of Pennsylvania, he commuted to Lanexa’s Park Avenue office from his new home in New Jersey. A Web site set up by his wife, Susan, shows pictures of a recent vacation to the Baseball Hall of Fame in Cooperstown, N.Y.

But last February, eight months before Mr. Rajaratnam and others were arrested and charged with insider trading, Mr. Hardin abruptly left Lanexa, according to former colleagues there. In October, two days after Mr. Rajaratnam was arrested and charged with insider trading, Mr. Hardin’s wife put a post on her Web site announcing the birth of their daughter, Molly.

Meanwhile, a federal judge on Tuesday afternoon denied Mr. Rajaratnam’s request to reduce his $100 million bail, siding with prosecutors who argued that he should not receive a reduction in bail.

Judge Richard J. Holwell made the ruling at a hearing in Federal District Court in Manhattan, where he also denied the prosecution’s request to detain Mr. Rajaratnam before his trial begins.