A former executive at the New Castle Funds LLC hedge fund pleaded guilty on Wednesday to an insider trading conspiracy that also ensnared Galleon fund founder Raj Rajaratnam, but he is not cooperating with the investigation.

The executive, Mark Kurland, 61, is the eighth person to plead guilty in Manhattan federal court in the probe of illegal trading involving the earnings forecasts and mergers and acquisitions of some of America's best-known companies.

At New Castle, Kurland was a colleague of Danielle Chiesi, 44, who was indicted along with Rajaratnam last month. Rajaratnam and Chiesi have pleaded not guilty to the charges. All three were arrested on October 16 last year.

U.S. prosecutors said that recorded telephone conversations between Rajaratnam and Chiesi revealed that Rajaratnam, Kurland, Chiesi and a cooperating witness received information directly or indirectly from insiders and provided it to each other for trading purposes.