Former SAC Capital employee Mathew Martoma (c.) exits Manhattan federal court with his lawyer, Charles Stillman, following an appearance on insider trading charges in New York November 26, 2012. REUTERS/Brendan McDermid

SAC Capital, the huge hedge fund accused this week of rampant insider trading, on Friday pleaded not guilty before a federal judge in New York City, CNBC reported.

CNBC said the plea will allow the Stamford, Conn.-based firm to keep operating. But early Friday a new figure emerged as an unlikely insider for the government's years-long investigation into the firm, resulting in multiple charges against SAC.

Former SAC portfolio manager Richard Lee, 34, pleaded guilty after a confidential hearing on insider trading that has threatened to blow open the investigation. Lee is currently cooperating with investigators in what is being described as the highest-profile insider trading case in history.

SAC, one of the most successful hedge fund firms in the country, with assets of about $15 billion, has been subjected to years of federal probes into suspected securities fraud dating back to 2006. Those investigations have resulted in charges being brought against 81 people since August 2009, resulting in 73 convictions and guilty pleas.

And last week the Securities and Exchange Commission filed a civil action against billionaire SAC chief Steven A. Cohen, accusing him of failing to supervise two employees who made insider trades.