The Office of Administrative Hearings may conduct hearings under this subtitle at correctional facilities in the Division of Correction or at the Patuxent Institution. With the approval of the Secretary, the Office of Administrative Hearings shall have access to documentary evidence of any person or facility that is the subject of an investigation or proceeding under this subtitle: at all reasonable times; and for the purpose of examining and copying the evidence. The Office of Administrative Hearings may issue subpoenas requiring: the attendance and testimony of witnesses; and the production of documentary evidence relating to any matter under investigation. The administrative law judge presiding at a hearing may administer oaths. A record of the testimony presented at the hearing shall be kept in accordance with regulations adopted by the Office of Administrative Hearings. The complainant has the right to appear before the Office of Administrative Hearings and to be represented by an attorney of the complainant’s choice at the complainant’s expense. The complainant shall have the opportunity to call a reasonable number of witnesses depending on the circumstances and the nature of the complaint, subject to the discretion of the Office of Administrative Hearings and the Inmate Grievance Office as to the relevance of the testimony and questions and the number of witnesses sought to be called. The complainant shall have a reasonable opportunity to question any witness who testifies before the Office of Administrative Hearings. The rights of the complainant under this subsection may not be unreasonably withheld or restricted by the Office of Administrative Hearings or the Inmate Grievance Office.