Does an inmate have an unrestricted right to present evidence at a disciplinary hearing?

An inmate does not have an unrestricted right to present evidence or to have all the witnesses he requests called at a disciplinary hearing. Wolff v. McDonnell, 418 U.S. 539, 566 (1974). "Prison officials must have the necessary discretion to keep the hearing within reasonable limits and to refuse to call witnesses that may create a risk of reprisal or undermine authority." Id. at 566. Should prison officials refuse to call a witness, they should explain their decision, but may do so either at the hearing, or "later." Id. at 497.