agena stated that he changed his story to say that he saw Moreno Morales shoot one of the victims, and the government then told him that he had “passed” the polygraph examination. Moreno Morales claims that the government only disclosed three polygraph examinations of Cartage-na to the defense, and alleges that the prosecutors committed misconduct by pressuring Cartagena.
Second, Moreno Morales has recently discovered that Cartagena gave three sworn statements during the Senate Investigation in late 1983 stating that he did not know who killed the victims at Cerro Ma-ravilla. These documents were never disclosed to the defense.
Finally, recent Senate notes that have been released reveal that witnesses Cart-agena and Montañez told the Senate during the 1983 investigation that they did not know who killed the independentistas. The notes show that United States Attorney Daniel López Romo and Assistant United States Attorney Celestino Matta were present during the questioning of Montañez and that Cartagena visited Ló-pez Romo after he was questioned. None of these statements were disclosed to the defense during Moreno Morales’s trial.
E. Current Petition
In August, 1998, Moreno Morales sought leave to file a second or successive petition under § 2255, alleging that newly-discovered evidence of witness recantation and prosecutorial misconduct warranted relief. Finding the circumstances “sufficiently unusual so as to ‘warrant a fuller exploration by the district court,’ ” we granted the application. Order of Court, No. 98-8025, Nov. 9, 1998 (citing Rodriguez v. Superintendent, Bay State Corr. Ctr., 139 F.3d 270, 272-73 (1st Cir.1998)). The district court then dismissed Moreno Morales’s § 2255 petition without an evidentiary hearing and subsequently issued a certifí-cate of appealability. This appeal followed.
II. Standard of Review
We review the district court’s dismissal of petitioner’s § 2255 motion de novo. Ellis v. United States, 313 F.3d 636, 641 (1st Cir.2002). Because the district court dismissed petitioner’s claim without an evidentiary hearing, we accept as true petitioner’s sworn factual allegations “unless those allegations are merely coneluso-ry, contradicted by the record, or inherently incredible.” Id.
III. Discussion
Evidentiary hearings on § 2255 petitions are the exception, not the norm, and there is a heavy burden on the petitioner to demonstrate that an evidentiary hearing is warranted. United States v. McGill, 11 F.3d 223, 225 (1st Cir.1993). An evidentiary hearing “is not necessary when a[§ ] 2255 petition (1) is inadequate on its face, or (2) although facially adequate, is conclusively refuted as to the alleged facts by the files and records of the case.” United States v. DiCarlo, 575 F.2d 952, 954 (1st Cir.1978) (quotation omitted).
A. Brady Claim
A defendant’s right to due process is violated when the prosecution suppresses evidence that is both favorable to the accused and material either to guilt or innocence. Brady v. Maryland, 373 U.S. 83, 87, 83 S.Ct. 1194, 10 L.Ed.2d 215 (1963). Impeachment evidence may make the difference between conviction and acquittal and, thus, must be disclosed. Giglio v. United States, 405 U.S. 150, 154, 92 S.Ct. 763, 31 L.Ed.2d 104 (1972). The accused does not have a duty to request favorable evidence from the prosecution.