An unidentified source familiar with the complaint revealed the information to The Associated Press on Thursday. The source was not authorized to speak publicly about the complaint and spoke on the condition of anonymity.
In the complaint, Blagojevich said he would put Candidate 4 in Barack Obama's vacant Senate seat instead of another candidate, if the governor did not get anything in return.
The complaint identified Senate Candidate 4 only as a "deputy governor."
Peters was named deputy governor in December 2006. She was previously Blagojevich's deputy chief of staff for social services and deputy campaign manager.