45 CFR § 681.28 - How is witness testimony presented?
(a) Except as provided in paragraph (b) of this section, testimony at the hearing shall be given orally by witnesses under oath or affirmation.
(b) At the discretion of the ALJ, testimony may be admitted in the form of a written statement or deposition. Any such statement must be provided to all other parties along with the last known address of such witness, in a manner which allows sufficient time for other parties to subpoena such witness for cross-examination at the hearing. Prior written statements of witnesses proposed to testify at the hearing and deposition transcripts shall be exchanged as provided in § 681.19.
(c) The ALJ shall exercise reasonable control over the mode and order of interrogating witnesses and presenting evidence.
(d) The ALJ shall permit the parties to conduct such cross examination as may be required for a full and true disclosure of the facts.
(e) Upon motion of any party, the ALJ shall order witnesses excluded from the hearing room so that they cannot hear the testimony of other witnesses. This rule does not authorize exclusion of -
(1) A party who is an individual;
(3) An individual whose presence is shown by a party to be essential to the presentation of its case, including an individual employed by the Government engaged in assisting the representative for the Government.