Yes, the FBI knew about the kickbacks and guess who was the FBI director at the time? Mueller!
If Mueller went forward with the charges during the reign of zero, I do not think it would have seen the light of day.
Lynch, her predecessor (mr just us hisself), the media and zero's personal flak takers would have endlessly paraded out in from of media to poo poo and discredit any such attempt before it got out of the lips of the announcers.