If the case is still open / active, there is contempt which the judge would have jurisdiction. Of course the case is presumed not open any longer....
At a minimum... one would expect perjury, and conspiracy to commit perjury. For those a federal prosecutor would be involved (calling Jeff Sessions) and who is the prosecutor going to trust in the apparently corrupted FBI to help in the investigation?
Seriously, the Postal Inspectors would be called in.
They are much more than just Mail Cops. They are the most skilled and uncorruptible federal LEOs, but few people know about them.
Through a Special Appointment, they could be brought in.