45 C.F.R. § 1174.15

(a) The investigating official, the reviewing official, and any employee or agent of the authority who takes part in investigating, preparing, or presenting a particular case may not, in such case or a factually related case:

(1) Participate in the hearing as the ALJ;

(2) Participate or advise in the authority head's review of the initial decision; or

(3) Make the collection of penalties and assessment.

(b) The ALJ must not be responsible to or subject to the supervision or direction of the investigating official or the reviewing official.