Neil Barofsky, the special inspector-general overseeing the US government's financial rescue efforts, is to probe allegations of insider trading among bank executives and their associates.
Eight of the largest banks in the US received between $2bn and $25bn in October 2008 under a programme to prop up the financial system led by Hank Paulson, then Treasury secretary.
Dozens more institutions followed and Mr Barofsky, who examines the troubled asset relief programme, is looking into whether information improperly made its way to trading rooms during a feverish period in which the government and banks were frequently exchanging information.