The subject of any hearing conducted under the provisions of this chapter may call witnesses on his behalf and at his expense. Such witnesses shall appear voluntarily and shall be limited to those persons who have knowledge of, or have specific testimony about, the factors which may have caused the hearing to be convened. The superintendent or his designee shall provide assistance to the inmate in notifying witnesses of the time and place of the hearing as requested by the inmate. The presiding officer may, in certain cases, direct the superintendent to make any staff member or prisoner available for testimony. For purposes of this section, family members and friends or other interested parties who wish to testify as to disposition may do so in writing. See WAC 381-60-090 for reference.