What is the test for suppressing or denying evidence in a civil case?

An individual's due process rights are violated if the government suppresses evidence which "was so important that its absence prevented the accused from receiving his constitutionally-guaranteed fair trial." United States v. Hibler, 463 F.2d 455, 459 (9th Cir.1972). The type of evidence in question here certainly meets that test. It can provide incontrovertible proof that the defendant is innocent of the heinous crime of rape and, as such, is "obviously of such substantial value to the defense that elementary fairness requires it to be disclosed even without a specific request." United States v. Agurs, 427 U.S. at 110, 96 S.Ct. at 2401.