It was, as we’ve repeatedly noted before, a Brady case and not a Mooney case.
But because Brady and Mooney are related, albeit distinct, Justice Stevens (who wrote the Agurs majority opinion) briefly discussed Mooney:
The rule of Brady v Maryland, 373 U. S. 83, arguably applies in three quite different situations. Each involves the discovery, after trial, of information which had been known to the prosecution but unknown to the defense.
In the first situation, typified by Mooney v. Holohan, 294 U. S. 103, the undisclosed evidence demonstrates that the prosecution’s case includes perjured testimony and that the prosecution knew, or should have known, of the perjury. In a series of subsequent cases, the Court has consistently held that a conviction obtained by the knowing use of perjured testimony is fundamentally unfair, and must be set aside if there is any reasonable likelihood that the false testimony could have affected the judgment of the jury. It is this line of cases on which the Court of Appeals placed primary reliance. In those cases the Court has applied a strict standard of materiality, not just because they involve prosecutorial misconduct, but more importantly because they involve a corruption of the truth-seeking function of the trial process. Since this case involves no misconduct, and since there is no reason to question the veracity of any of the prosecution witnesses, the test of materiality followed in the Mooney line of cases is not necessarily applicable to this case.
Let’s put it another way: the Agurs case says absolutely nothing of any importance about Mooney. It certainly does not establish that Mooney has a “materiality” requirement because in the highlighted passage it explicitly tells us that everything it is saying about Mooney is dicta.
Mooney was a landmark due process case. It is not to be limited or qualified by dicta in subsequent cases that are really about something else. Which Agurs was. Namely Brady, not Mooney.
Nevertheless, it is one of the ironies of this whole sordid tale that Justice Stevens’ opinion in Agurs wound up being a significant contributor to the serious confusion around the country on this Brady-Mooney business that we, and we alone it sometimes seems, have had to contend with. The reason for the irony is that Justice Stevens later wrote very powerful – and in our opinion unarguably correct – dissents in two other cases where Justices who fundamentally disagreed with him capitalized on this Agurs mistake: United States v. Williams and Albright v. Oliver.