solely on the recantation of a prosecution witness would have been regarded at common law as a violation of fundamental law. Moreover, in this case Portas’s recantation testimony did not affirmatively exonerate Landano but merely called into question the validity of Portas’s identification of Landano. In these circumstances, the district court’s deference to the state court’s assessment of Portas’s recantation was not unconstitutional.
B.
Landano asserts that habeas relief must be granted because the prosecution violated the Brady standard by withholding from the defense certain information concerning Allen Roller.
At trial, Roller testified that he had plead non vult to a felony murder charge in connection with the robbery of the check cashing service. He also testified that he was cooperating with the State pursuant to assurances that he would not receive a sentence in excess of thirty years and that the State would dismiss charges against him stemming from the robbery of a Jersey City bar. He did not allude to any other charges pending against him. Roller admitted that Victor Forni had participated in the planning of the Kearny robbery, but he denied that Forni had played any role in the execution of the crime. Roller also denied having participated with Forni in other crimes.
After the trial, it came to light that Roller had been linked to two armed robberies in Perth Amboy, New Jersey, that occurred before the Kearny robbery. Lan-dano moved for a new trial on the basis of this information. After holding hearings, the trial court found that before Landano’s trial a witness to the Perth Amboy robberies had tentatively identified Roller, Forni, and Bruce Reen as possible perpetrators of those crimes. The court also found that the prosecutor in Landano’s case had had constructive knowledge of the information linking Roller to the Perth Amboy robberies.
The prosecution’s non-disclosure of evidence amounts to a Brady violation only if the evidence is both exculpatory and material. Evidence is “material” in this context “if there is a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different. A ‘reasonable probability’ is a probability sufficient to undermine confidence in the outcome.” United States v. Bagley, 473 U.S. 667, 682, 105 S.Ct. 3375, 3383, 87 L.Ed.2d 481 (1985) (opinion of Blackmun, J., joined by O’Connor, J.); accord id. at 685 (opinion of White, J., joined by Burger, C.J., and Rehnquist, J.) (agreeing with Justice Blackmun’s definition of materiality).
The district court determined that the evidence of Roller’s possible participation in the Perth Amboy robberies was exculpatory, but the court went on to hold that the evidence was not material. Accordingly, the court concluded that no Brady violation had occurred. Whether evidence is material for purposes of the Brady analysis is a mixed question of law and fact. Carter v. Rafferty, 826 F.2d 1299, 1306 (3d Cir.1987), cert. denied, — U.S. —, 108 S.Ct. 711, 98 L.Ed.2d 661 (1988).
We agree with both parts of the district court’s analysis. The evidence was exculpatory because the defense could have used it to impeach Roller on cross-examination, see Giglio v. United States, 405 U.S. 150, 154, 92 S.Ct. 763, 766, 31 L.Ed.2d 104 (1972), and perhaps also as substantive evidence that Roller and Forni generally operated together, see N.J. R.Evid. 55. The evidence was relevant both to Roller’s credibility and to Landano’s defense that Forni, rather than Landano, had accompanied Roller during the robbery and had murdered Officer Snow.
Nevertheless, we do not believe that the evidence was material under the Bagley standard. Roller was presented to the jury as a convicted felon, so evidence tending to link him with another crime would have had at best a marginal effect on the jury’s assessment of his general credibility. The materiality question is a somewhat closer one to the extent that the evidence would have permitted an inference that Roller and Forni operated together on other occasions