28 C.F.R. § 76.29 – Witnesses.

(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 Judge and to the extent otherwise permitted by law, testimony may be admitted in the form of a written statement or deposition. Any such written 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, if necessary, 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 28 CFR 76.22.
(c) The Judge shall exercise reasonable control over the mode and order of interrogating witnesses and presenting evidence so as to:
1. (1) Make the interrogation and presentation effective for the ascertainment of the truth;
2. (2) Avoid needless consumption of time; and
3. (3) Protect witnesses from harassment or undue embarrassment.
(d) The Judge shall permit the parties to conduct such cross-examination as may be required for a full and true disclosure of the facts.
(e) At the discretion of the Judge, a witness may be cross-examined on matters relevant to the proceeding without regard to the scope of his or her direct examination.
(f) Upon motion of any party, the Judge shall order witnesses excluded so that they cannot hear the testimony of other witnesses. This part does not authorize exclusion of the following:
1. (1) The respondent;
2. (2) An individual whose presence is shown by a party to be essential to the presentation of its case.