The executive director over an Arkansas pension fund has retained outside counsel but insisted he could continue to serve as lead plaintiff in settlements with State Street Corp. despite an overbilling probe that could end up returning a “significant amount of money” to class members, according to a federal judge’s remarks.

In an affidavit filed on Wednesday, George Hopkins, executive director of the Arkansas Teacher Retirement System, said he had retained Thomas Hoopes of Boston’s LibbyHoopes, who represents professionals in criminal matters and corporate investigations.