The person spoke on condition of anonymity to protect the identity of a client who has been questioned in the probe. The case, which has been assigned to two federal prosecutors and two FBI agents in Delaware, has not been brought before a grand jury.
O'Donnell, who set a state record by raising more than $7.3 million in an unsuccessful U.S. Senate campaign this year, has been dogged by questions about her finances.
Her former campaign manager did not immediately respond Wednesday to questions.
