HANSEN, Circuit Judge.
Robert Allan Cornell (Cornell), an Iowa prisoner, brings this habeas corpus action pursuant to 28 U.S.C. § 2254. We conclude that Cornell is not entitled to habeas relief.
I. FACTS AND PROCEDURAL HISTORY
Cornell was convicted after a jury trial of the 1976 first degree murder of Kenneth Crow (Crow). See Iowa Code §§ 690.1, 690.2 (1975). He was sentenced to a term of life imprisonment without parole. See Iowa Code § 690.2 (1975).
Cornell’s thirteen-year-old half brother, Glen Albert Oliver (Albert), was the primary witness against Cornell. Albert testified that he, Cornell, and Crow returned to Des Moines, Iowa, from a trip to San Antonio, Texas, on August 29-30, 1976. According to Albert, they stopped at a wooded area along Interstate 35 in southern Iowa on the morning of August 30th. Albert testified that Cornell and Crow left the vehicle for the stated purpose of shooting a cow. Cornell took a .38 caliber pistol with him. Albert then heard a shot, and Cornell returned alone. Albert further testified that “I asked [Cornell] if he did what I think [sic] he did and he said, ‘Yes, does it bother you?’ ” Transcript of trial (trial tr.), vol. I, at 39. Albert did not testify that he actually saw Cornell shoot Crow. Albert informed the authorities of these events four days later and led the authorities to Crow’s body. Crow had been shot once in the back of his head. In his defense, Cornell testified that Crow had left the car alive after an argument with Cornell and had stolen Cornell’s gun. The primary defense strategy was to impeach Albert’s testimony with his prior inconsistent statements and with inconsistencies between his testimony and the physical evidence. The defense also theorized that Sheldon Bryce Oliver (Bryce or Bryce Oliver), Albert’s brother, had killed Crow and had dumped the body along the interstate. The defense also emphasized that there was no physical evidence tying Cornell to the murder scene. Eric Lynn Cross (Cross) testified that shortly after the trip to Texas, Cornell told him that “we didn’t have to worry about Kenny, because that Kenny had tried to shoot him and he [Cornell] broke his neck.” Trial tr., vol. II, at 83. Bryce Oliver testified that Cornell made a similar statement to him.
Cornell’s conviction and sentence were affirmed on direct appeal. See State v. Cornell, 266 N.W.2d 15 (Iowa), cert. denied, 439 U.S. 947, 99 S.Ct. 340, 58 L.Ed.2d 338 (1978). Cornell’s first federal habeas petition was denied. Cornell v. Iowa, 628 F.2d 1044 (8th Cir.1980), cert. denied, 449 U.S. 1126, 101 S.Ct. 944, 67 L.Ed.2d 112 (1981). In that petition, Cornell raised, inter alia, the question of whether the trial judge’s inquiry into the numerical standing of the jury after several hours of deliberation and the giving of an Allen1 charge constituted error. The jury had deadlocked at 7-5 but eventually reached a verdict after the Allen charge and six more hours of deliberation. Although expressing concern regarding the procedures followed by the trial judge, the majority of the panel found no violation of Cornell’s constitutional rights. Cornell, 628 F.2d at 1048.
In 1981 Cornell filed an application for postconviction relief under Iowa Code Chapter 663A. He first asserted that several items of exculpatory evidence had been suppressed by the prosecution. He also presented newly discovered evidence suggesting that Bryce killed Crow. Finally, he claimed ineffective assistance of trial counsel. See Cornell v. State, No. 3453 (Iowa Dist.Ct. for Clarke County Dec. 15, 1986). The postconviction trial court de[379]*379nied Cornell’s application in a lengthy and thorough opinion. The Court of Appeals of Iowa found that the prosecutor’s suppression of exculpatory evidence denied Cornell a fair trial and then reversed and remanded for a new trial in a 3-2 decision. See Cornell v. State, No. 87-69 (Iowa Ct.App. Apr. 20, 1988). The exculpatory evidence upon which the court of appeals based its decision included: (1) a statement from Jody Seidenkranz (Seidenkranz) to Special Agent Robert Pontious of the Iowa Bureau of Criminal Investigation on October 6, 1976, that Cornell had told her when he returned from Texas that Crow had left the car and stolen Cornell’s gun and that Albert had agreed with Cornell’s statement; and (2) a statement from Bryce Oliver to Special Agent Pontious on September 29, 1976, that four days before Crow left for Texas they had had a fight and Bryce had taken out a razor scraper and threatened Crow. The Supreme Court of Iowa, in a unanimous decision, reversed the court of appeals, finding that the suppressed evidence was not material because a reasonable probability did not exist that the disclosure of the evidence would have changed the result of the trial. See Cornell v. State, 430 N.W.2d 384, 386 (Iowa 1988).
At the state postconviction hearing held in October of 1985, Cornell’s counsel offered two signed but unsworn statements made by Cross in October of 1977. In those statements Cross recanted his trial testimony and implicated Bryce Oliver in Crow’s death. Cross was not called to testify at the postconviction hearing because he was incarcerated in Missouri at the time. Cross’s hearsay statements were admitted by the court, not as proof of the truth of the assertions therein, but only as proof that the statements were made and transmitted to the authorities. Special Agent Robert Pontious testified that he had investigated the statements made by Cross and that during an interview with Cross on November 30, 1977, at the Iowa Men’s Reformatory, Cross had informed Pontious that Cornell had intimidated him into making the recantation statements and that the statements were not true. Following the interview with Cross, Special Agent Pontious concluded that further investigation was not warranted. Cornell did not explicitly argue in his state postconviction action that Cross’s 1977 recantation statements constituted newly discovered evidence that warranted a new trial.
Cornell filed the pending habeas corpus petition on November 9, 1988, and raised the suppression of the allegedly exculpatory evidence but did not raise any claim based on Cross’s 1977 recantation. On February 6, 1989, Cornell amended his petition and alleged that additional exculpatory evidence, including Cross’s 1977 recantation, had been suppressed by the prosecution. On February 28, 1989, Cornell’s counsel obtained an affidavit from Cross. In the 1989 affidavit, Cross recants his trial testimony and asserts that he never heard Cornell say anything about harming Crow. Cross does state that he did not hear everything that Cornell said to Bryce. Cross also denied being visited by Pontious at the Reformatory in 1977. Cornell moved to supplement the record with Cross’s 1989 recantation affidavit. The state resisted on the basis that there was no documentation of the efforts made to offer this evidence in the state postconviction proceedings. The district court denied Cornell’s request to supplement the record with Cross’s affidavit.
On December 17, 1990, a panel of this court remanded this case to the district court for an evidentiary hearing on the issue of whether Cross’s recantation of his trial testimony was newly discovered evidence warranting a new trial. See Cornell v. Nix, 921 F.2d 769, 771 (8th Cir.1990). On August 20, 1991, following an evidentiary hearing,2 the district court certified its find[380]*380ings of fact and conclusions of law. The district court concluded:
It is also reasonable to believe that had the jury in petitioner’s trial, which deadlocked 7-5 after fifteen hours of actual deliberation and reached a verdict of guilty only after receiving an “Allen charge” from the judge and deliberating nearly six more hours, would probably have found petitioner not guilty if the type of evidence presented to me at the remand hearing and the suppressed exculpatory evidence (Jody Seidenkranz’s October 6, 1976, statement and Sheldon Bryce Oliver’s September 29, 1976, statement) had been presented to that jury. I believe that it is reasonably probable that if there is a retrial and all of this evidence is presented to the jury, the petitioner will be found not guilty.
District court’s certified findings and conclusions, filed August 20, 1991, at 6. The district court declined to address the state’s procedural default argument on the grounds that that issue was outside of the scope of the limited remand.
Following the district court’s certification of its findings of fact and conclusions of law, the panel concluded that Cornell had demonstrated cause and prejudice for his procedural default in failing to raise earlier the issue of Cross’s recantation and remanded with instructions to grant the writ subject to a new trial. See Cornell v. Nix, 953 F.2d 1103 (8th Cir.1992). We vacated the panel’s decision and granted rehearing en banc. We now conclude that Cornell has not demonstrated cause for his procedural default with respect to his claim based on Cross’s recantation. We also address Cornell’s claim that certain exculpatory evidence was suppressed by the prosecution. We conclude that the allegedly suppressed exculpatory evidence was not material.
II. CROSS’S RECANTATION
The state argues that Cornell’s claim based on Cross’s more recent recantation is procedurally barred by Cornell’s failure to raise this claim in a timely fashion in the state courts.
A claim not raised in the state courts will not be considered by a federal habeas court unless the petitioner can demonstrate cause for his previous failure to raise the claim and prejudice. See Wainwright v. Sykes, 433 U.S. 72, 87, 97 S.Ct. 2497, 2506, 53 L.Ed.2d 594 (1977). Recently, the United States Supreme Court held that the cause and prejudice standard should also be used to evaluate whether a petitioner should be excused from his failure to develop a material fact in state court proceedings. See Keeney v. Tamayo-Reyes, — U.S. -, 112 S.Ct. 1715, 118 L.Ed.2d 318 (1992).
“[Cjause ... ordinarily requires a showing of some external impediment preventing counsel from constructing or raising the claim.” Murray v. Carrier, 477 U.S. 478, 492, 106 S.Ct. 2639, 2647, 91 L.Ed.2d 397 (1986). An external impediment can be “the reasonable unavailability of the factual basis for the claim.” McCleskey v. Zant, — U.S.-,-, 111 S.Ct. 1454, 1472, 113 L.Ed.2d 517 (1991). See also Murray, 477 U.S. at 488, 106 S.Ct. at 2645. “If what petitioner knows or could discover upon reasonable investigation supports a claim for relief in a federal habeas petition, what he does not know is irrelevant. Omission of the claim will not be excused merely because evidence discovered later might also have supported or strengthened the claim.” McCleskey, — U.S. at-, 111 S.Ct. at 1472. We also note that one aspect of the test for newly discovered evidence is whether the evidence could have been discovered earlier in the exercise of due diligence. See United States v. Bednar, 776 F.2d 236, 238 (8th Cir.1985).
Applying these standards, we find that the factual basis for Cornell’s claim based on Cross's recantation was reasonably available to petitioner at the time of his state postconviction hearings. Postconviction counsel knew that Cross had previously recanted in 1977. Counsel knew that Cross was incarcerated in Jefferson City, Missouri. See transcript of October 9, 1985, postconviction hearing at 204. There is nothing in the record that suggests that counsel could not have obtained Cross’s [381]*381recantation, through an affidavit, deposition, or other means, for the postconviction hearing.3 There is nothing in the record that suggests that counsel made any attempt to contact Cross. We note that the postconviction trial court held evidentiary hearings on October 9-10, 1985; November 13, 1985; January 8-9, 1986; January 23, 1986; February 18, 1986; May 1, 1986; and June 5, 1986. It appears from our review of the record that the postconviction trial court gave Cornell every opportunity to obtain evidence in support of his claims. We find no due diligence here.
In Coleman v. Thompson, — U.S. -, -, 111 S.Ct. 2546, 2566, 115 L.Ed.2d 640 (1991), the United States Supreme Court held that there is no cognizable habeas claim for ineffective assistance of postconviction counsel because no constitutional right to counsel exists in postcon-viction proceedings. Thus, postconviction counsel’s failure to more fully investigate the potential of Cross’s recantation cannot constitute “cause.”
Because we find that Cornell has not demonstrated cause for his procedural default, we need not address the issue of prejudice.
A narrow exception to the cause and prejudice standard exists. A procedural default will be excused if petitioner can demonstrate that a fundamental miscarriage of justice will occur from the federal court’s refusal to entertain the claim. See Tamayo-Reyes, — U.S. at-, 112 S.Ct. at 1721; Murray, 477 U.S. at 495-96, 106 S.Ct. at 2649-50. In order to fall within this exception, petitioner must demonstrate that “a constitutional violation has probably resulted in the conviction of one who is actually innocent.” Murray, 477 U.S. at 496, 106 S.Ct. at 2649. Recently, the United States Supreme Court refined the “actual innocence” standard and held that “to show ‘actual innocence’ [of the death penalty] one must show by clear and convincing evidence that but for a constitutional error, no reasonable juror would have found the petitioner eligible for the death penalty.” Sawyer v. Whitley, — U.S.-,-, 112 S.Ct. 2514, 2517, 120 L.Ed.2d 269 (1992). This new standard also applies to habeas challenges to convictions. McCoy v. Lockhart, 969 F.2d 649 (8th Cir.1992).
The district court concluded that if Cross’s recantation and the statements from Jody Seidenkranz and Bryce Oliver were presented to a jury on retrial, there is a reasonable probability that the jury would acquit Cornell. Although this conclusion is not entirely equivalent to a finding of “actual innocence,” we must address the question of whéther this statement by the district court is a factual finding of actual innocence subject to a clearly erroneous review or whether this conclusion should be reviewed de novo. We have located no authority in the case law discussing what standard of review applies to a conclusion of actual innocence.
In Sawyer, the Supreme Court appears to apply a de novo standard to the issue of whether Sawyer had demonstrated actual innocence. Sawyer, — U.S. at- -, 112 S.Ct. at 2523-25. In a somewhat related context, we have applied a de novo review to the ultimate conclusion of mixed questions of law and fact, although predicate factual findings are reviewed for clear error. See, e.g., Bliss v. Lockhart, 891 F.2d 1335, 1339 (8th Cir.1989) (reviewing de novo ultimate finding of ineffective assistance of counsel, which requires showing that but for counsel’s unprofessional errors, the result of the proceeding would have been different). Accordingly, we consider the question of actual innocence de novo.
Cross’s testimony was a small part of the evidence against Cornell. It was not, in our view, crucial to the prosecution’s ease. Bryce also testified that Cornell had made the statements which Cross attributed to Cornell. The testimony of Albert was the crucial testimony against Cornell.4 [382]*382Cross’s recantation does not directly cast any further doubt on Albert’s testimony. As discussed later in this opinion, we do not find the statements from Jody Seidenkranz and Bryce Oliver to be material under Brady v. Maryland, 373 U.S. 83, 87, 83 S.Ct. 1194, 1196-97, 10 L.Ed.2d 215 (1963), and United States v. Bagley, 473 U.S. 667, 682, 105 S.Ct. 3375, 3383, 87 L.Ed.2d 481 (1985). Accordingly, we do not find that Cornell has demonstrated by clear and convincing evidence that but for the alleged errors, no reasonable juror would have convicted him.5
III. SUPPRESSED EXCULPATORY EVIDENCE
In order to obtain habeas relief on his claim of improperly suppressed exculpatory evidence, Cornell must show: (1) the prosecution suppressed evidence; (2) the evidence was favorable to him; and (3) the evidence was material to the issue of guilt. See Brady v. Maryland, 373 U.S. 83, 87, 83 S.Ct. 1194, 1196-97, 10 L.Ed.2d 215 (1963). With regard to the first two prongs of the test, the state courts found that the prosecution did suppress the October 6, 1976, statement from Jody Seidenkranz and the September 29, 1976, statement from Bryce Oliver and that that evidence was favorable to Cornell’s defense. We accept those findings. See 28 U.S.C. § 2254(d).6
Suppressed exculpatory “evidence is material only 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). The Supreme Court of Iowa concluded that the statements from Seidenkranz and Bryce were not material because there was no reasonable probability that the result of the trial would have been different. Cornell, 430 N.W.2d at 386. The supreme court reasoned that the only use for Seid-enkranz's statement would have been to impeach Albert and that Albert’s testimony was impeached through the use of several prior inconsistent statements. Id. The court further noted that Albert’s acquiescence in Cornell’s statements could easily be explained by threats made by Cornell against Albert, which Albert had testified to at trial. Id. With regard to the statement by Bryce Oliver, the Supreme Court of Iowa reasoned that the statement would have impeachment value because Bryce had denied at trial threatening Crow with the razor scraper. Id. During his testimony, Cornell had testified concerning the threat made by Bryce against Crow. Id. The court also noted that this evidence would have bolstered Cornell’s theory that Bryce killed Crow. Id. The court concluded, however, that a reasonable probability did not exist that the exclusion of Bryce’s statement would have changed the result of the trial. Id.
A state court's determination regarding materiality under Brady is a mixed question of law and fact which is not entitled to the presumption of correctness under 28 U.S.C. § 2254(d). See, e.g., Carter v. Rafferty, 826 F.2d 1299, 1306 (3d Cir.1987), cert. denied, 484 U.S. 1011, 108 S.Ct. 711, 98 L.Ed.2d 661 (1988); Bowen v. Maynard, 799 F.2d 593, 610 (10th Cir.), cert. denied, 479 U.S. 962, 107 S.Ct. 458, 93 [383]*383L.Ed.2d 404 (1986). After considering this matter de novo, we agree with the Supreme Court of Iowa that the suppressed evidence was not material.
The sole use of Seidenkranz’s statement would have been to further impeach Albert. Albert was extensively cross-examined by counsel with his numerous previous inconsistent statements. The post-conviction trial court found that Cornell’s attorney had “compiled numerous inconsistent statements of Albert Oliver on virtually every important point of his anticipated testimony” and had “prepared an elaborate cross-examination for Albert Oliver,” and that his “planned impeachment of Albert Oliver was presented to the jury through a thorough cross-examination.” Cornell, No. 3453, slip op. at 4-5. A reading of the murder trial transcript confirms those findings. Further, Albert testified that he was afraid of Cornell because Cornell had threatened to kill him if he told anyone. The jury was aware that Albert did not tell anyone of Crow’s murder until several days after it happened.
We note the following testimony by Albert:
Q. When you got up to your mom’s place, what did you do?
A. ... [W]e got out of the jeep and I just walked on up and so did Bobby and she asked where Crow was and Bobby said that he got mad and got out of the jeep and had stole his gun.
Q. Did you talk to Bob anymore in the week about this incident with Mr. Crow?
A. He kept on coming over to my house and asking everybody if they had seen Crow, and everybody just kept on telling him no; and he just told me to remember what he’d told me.
Q. What do you mean, “remember what he told me”?
A. He had told me if I told anybody he would kill me, too.
Trial tr., vol. I at 41-42.
This testimony demonstrates that the jury was aware that Albert had initially acquiesced in Cornell’s version of the events due to his fear of Cornell. Although the record is less than entirely clear, we find that the incident with Albert’s mother, Alberta Garner, is probably the same incident referred to by Jody Seid-enkranz (Albert’s sister) in her statement. This additional item of cumulative impeachment material does not raise a reasonable probability that the outcome of the trial would have been different.
Special Agent Pontious’s report of his September 29, 1976, interview with Bryce Oliver states the following:
The reporting agent questioned BRYCE OLIVER regarding a possible threat he had made towards KENNETH CROW prior to the time ROBERT CORNELL, KENNETH CROW and ALBERT OLIVER left for San Antonio, Texas.
BRYCE went on to state that approximately four days before they left for Texas ... he and KENNY became involved in some type of argument at which time he took out a razor scraper which he carried in his pocket and made threats towards KENNY however, he stated that this was not unusual and that there was no intent in the threat.
At trial, Cornell testified that he was present at the argument between Bryce and Crow and that Bryce had pulled a razor knife and threatened to cut Crow up. Bryce testified at trial as follows:
Q: Did you have an argument with [Crow] shortly before he went to Texas?
A: Yes.
A: We got in an argument because there had been a break in at Industrial [Janitorial Services] and he said that Eric and I were trying to set him up for it, and make him look like he did it; and we had an argument about it.
Q: This is the argument you called a friendly argument?
A: I have arguments with friends of mine all the time, but as long as it ain’t a fist fight or something, I feel it’s just an argument between friends.
Q: You threatened him at the time? At the time you had the arguments, didn’t you threaten him?
[384]*384A: I don’t recall.
Trial tr., vol. Ill, at 12-13. At his pretrial deposition, Bryce had testified as follows:
Q. Did you have a knife with you that day?
A. Yes.
Q. Did you pull that out?
A. No. If I pull a knife on somebody I’m going to use it, I’m going to carve them up. I’m not going to threaten nobody, it will be action.
Q. Did you threaten him that day with a knife?
A. I threatened to bust his head.’
Deposition of Bryce Oliver at 118, as read during the February 18, 1985, evidentiary hearing at 51.
We first note that at trial Bryce did not deny threatening Crow. He testified that he did not recall whether or not he had. We also note that counsel did not impeach Bryce with his pretrial deposition testimony that he had threatened to bust Crow’s head. The impeachment value of Bryce’s statement to Special Agent Pontious is minimal. Further, although this evidence would have supported Cornell’s theory that Bryce killed Crow, it does not conclusively prove either that Bryce actually killed Crow or that Cornell did not kill Crow. Finally, this evidence would not have affected the credibility of Albert’s testimony. Accordingly, we find that there is not a reasonable probability that the disclosure of Bryce’s statement would have affected the outcome of the trial.
IV. CONCLUSION
We conclude that petitioner has not shown cause for his procedural default in failing to present his claim based on Cross’s recantation to the state courts. We further conclude that the suppressed exculpatory statements of Jody Seiden-kranz and Bryce Oliver are not material under Brady and Bagley.
Accordingly, we remand this matter to the district court with instructions to deny Cornell’s application for writ of habeas corpus.