U.S. securities regulators have added a charge against a research analyst, who it accuses of providing inside information, in the SAC Capital insider trading case.

The U.S. Securities and Exchange Commission (SEC) brought charges Tuesday against an analyst, who it says tipped confidential information to an SAC portfolio manager, who has himself already been charged with insider trading. The SEC amended its complaint against Richard Lee, an SAC portfolio manager, who was charged last week, to additionally charge Sandeep Aggarwal, a sell-side analyst who the SEC accuses of tipping Lee in advance of a July 2009 public announcement.

In a parallel action, the U.S. Attorney’s Office for the Southern District of New York also announced criminal charges against Aggarwal Tuesday. The allegations in both cases have not been proven.

The SEC alleges that Aggarwal learned confidential details about the significant progress of negotiations to finalize a search engine partnership between Microsoft and Yahoo. It says that he learned inside information on the talks from a close friend at Microsoft on July 9, 2009, and he tipped Lee with the information during a telephone call the following day. It says that Lee then purchased large amounts of Yahoo stock in the hedge fund that he managed, as well as in his personal trading account on the basis of the inside information.

When the information was reported in the media almost a week later, Yahoo’s stock price rose approximately 4%, it says, adding that SAC Capital and Lee reaped substantial profits from the Yahoo shares that he purchased after speaking to Aggarwal.

The SEC’s amended complaint seeks a final judgment ordering Aggarwal and Lee to pay disgorgement of ill-gotten gains plus prejudgment interest and financial penalties, and permanently enjoining them from future violations of these provisions of the federal securities laws. The regulator notes that its investigation is continuing.

“Rather than rely on legitimate research methods, Aggarwal obtained confidential information from a close friend at Microsoft and passed it along to Lee knowing that he would likely trade on it,” said Sanjay Wadhwa, senior associate director of the SEC’s New York Regional Office. “As a sell-side analyst, Aggarwal knew the rules and yet he broke them, which is why he joins the growing ranks of those held accountable by the SEC for insider trading.”