Billionaire investor Steven Cohen received a subpoena to testify before a grand jury in connection with the United States government’s insider trading investigation against his hedge fund, SAC Capital Advisors, as reported by Ben Protess and Peter Lattman of the New York Times.

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The latest move of the authorities showed that they are intensifying their criminal investigation to build up a strong case against SAC Capital Advisors and its executives. The subpoena includes other names of executives, and the hedge fund was also required to submit information regarding its activities.

Last Friday, SAC Capital Advisors warned investors that its cooperation with government’s insider trading investigation is no longer conditional, and there would be more clarity regarding the issue through 2013.

The hedge fund issued a disclosure letter to investors after meeting with prosecutors. Charlie Garparino of FOX Business cited sources that SAC Capital Advisors failed to reach a settlement agreement to close the insider trading investigation.

According to a lawyer familiar with the situation, Cohen might claim his constitutional right against self-incrimination instead answering different questions on a wide range of topics before the grand jury. A formal indictment from prosecutors generally proceeds after a grand jury testimony.

One of Gasparino’s sources commented, “Steve is not giving up on his business. We’ll have to see how this turns out.” The source believe that Cohen will use a different legal strategy such as preventing self-incrimination given the fact that the company will no longer cooperate with the government investigation. Gasparino wonders if Cohen’s fetish for art got him in trouble with the government. He tweeted that SAC insiders thought that the firm had a deal with the feds to end the probe, but it seemed that authorities dumped the deal after Cohen’s art buy.

SAC Capital Advisors agreed to pay a fine of $616 million to settle the complaint of the Securities and Exchange Commission (SEC) in connection with its insider trading activities of its former portfolio manager, Mathew Martoma involving the shares of Wyeth Limited (NSE:WYETH) (BOM:500095) and Elan Corporation, plc (NYSE:ELN). The settlement required a court approval. Martoma pleaded not guilty with the insider trading charges filed against him.

The Federal Bureau of Investigation (FBI) arrested Michael Steinberg, portfolio manager of SAC Capital Partners and charged him with four counts of securities fraud and conspiracy to commit securities fraud. He was accused of committing illegal trades involving the shares of Dell Inc. (NASDAQ:DELL) and NVIDIA Corporation (NASDAQ:NVDA).