What is the test for a prison to deny a prisoner access to documentary evidence in their own defense?

We have held that a prisoner's right to call a witness in a disciplinary process, as articulated in Wolff, means that the prison may not impose a prohibition on witnesses being present to testify. Mitchell v. Dupnik, 75 F.3d 517, 525 (9th Cir. 1996) ("[A] blanket denial of permission for an inmate to have witnesses physically present during disciplinary hearings is impermissible, even where jail authorities provide for interviewing of witnesses outside the disciplinary procedure."). The same is true with documentary evidence. The right referenced in Wolff to "present documentary evidence in" the prisoner's own defense must generally include the ability to obtain that documentary evidence in the first place. Wolff, 418 U.S. at 566. Similarly, if a prisoner is to be able to respond to evidence presented against him, as a general proposition he should be allowed to know what it is and to examine it, unless there is reason to the contrary.

To be clear, a prisoner's right to access and prepare evidence for a disciplinary hearing is not unlimited nor unfettered. It may be limited by prison officials if they have a "legitimate penological reason." Koenig v. Vannelli, 971 F.2d 422, 423 (9th Cir. 1992). If granting a prisoner access to the requested evidence would "be unduly hazardous to institutional safety or correctional goals," access may be denied. Wolff, 418 U.S. at 566.