The chairman of the US senate judiciary committee said the conduct of the Securities and Exchange Commission in its investigation of alleged insider trading at hedge fund Pequot is "very, very troubling" and Congressional reviews will continue.

Gary Aguirre, a former investigator at the SEC, alleged that he was fired by the regulator because he wanted to question John Mack, the chairman and chief executive of Morgan Stanley, as part of the investigation and was told he could not issue a subpoena because of Mack's powerful political connections.