Appellant seeks reversal of the trial court’s decision to deny without a hearing *234his § 23-1101 motion alleging ineffective assistance of counsel. We affirm.
In 1980, after a jury trial, appellant was convicted of second-degree murder while armed, assault with a dangerous weapon, and carrying a pistol without a license. A summary of the evidence presented at appellant’s trial is set forth in this court’s opinion affirming his convictions. Ready v. United States, 445 A.2d 982 (D.C.1982), cert. denied, 460 U.S. 1025, 103 S.Ct. 1279, 75 L.Ed.2d 498 (1983). In 1991, appellant filed a motion alleging ineffective assistance of counsel based primarily on the ground that his trial counsel failed to secure at trial the presence of Mandell Cooper, an eyewitness who appellant claims would have presented exculpatory testimony.2 The trial court denied appellant’s motion without a hearing. We now consider both the trial court’s decision not to hold a hearing and the decision to deny the claim.
There is a presumption in favor of holding a hearing on a § 23-110 motion alleging ineffective assistance of counsel that requires an inquiry into matters outside the record. Gaston v. United States, 535 A.2d 893, 898 (D.C.1988); Gibson v. United States, 388 A.2d 1214, 1216 (D.C. 1978). However, the filing of such a § 23-110 motion does not automatically require the trial court to conduct a hearing. Gibson, supra, 388 A.2d at 1216-17. Where the existing record provides an adequate basis for disposing of the motion, the trial court may rule on the motion without holding an evidentiary hearing. D.C.Code § 23-110; Ellerbe v. United States, 545 A.2d 1197, 1198-99 (D.C.), cert. denied, 488 U.S. 868, 109 S.Ct. 174, 102 L.Ed.2d 144 (1988). Moreover, the court has recognized that a hearing is unnecessary when the motion consists of (1) vague and conclusory allegations, (2) palpably incredible claims, or (3) allegations that would merit no relief even if true. Ramsey v. United States, 569 A.2d 142, 147 (D.C.1990) (citation omitted).
To prevail on a claim of ineffective assistance of trial counsel, the claimant must demonstrate two things: (1) deficient performance on the part of his trial counsel, and (2) prejudice as a result of that deficient performance. Strickland v. Washington, 466 U.S. 668, 687, 104 S.Ct. 2052, 2064, 80 L.Ed.2d 674 (1984). In considering the first, “[¡judicial scrutiny ... must be highly deferential_ [A] Court must indulge a strong presumption that counsel’s conduct falls within the wide range of reasonable professional assistance.” Id. at 689, 104 S.Ct. at 2065. In considering the second, the court must find that appellant has shown “there is a reasonable probability that, but for counsel’s unprofessional errors, the result [at trial] would have been different.” Id. at 694, 104 S.Ct. at 2068.
We conclude that appellant’s motion, which was based on the unsubstantiated assertion that he suffered prejudice as a result of his trial counsel’s decision not to call Cooper as a witness, was too speculative to warrant a hearing. Since appellant’s motion was deficient as to the prejudice prong of Strickland, we need not reach the issue of his counsel’s deficient performance. See, e.g., Griffin v. United States, 598 A.2d 1174, 1176 (D.C.1991) (“Strickland ... suggests] that it is sometimes efficacious to address the prejudice prong first since without prejudice there can be no ineffective assistance of counsel.”); Strickland, supra, 466 U.S. at 697, 104 S.Ct. at 2069. Therefore, we hold that the trial court did not err in denying appellant a hearing on the basis of the information then available to the trial court.
*235The basis for appellant’s allegation of prejudice rests solely on the fact that Cooper was identified as a Brady3 witness by the government. However, appellant has not offered a credible indication as to what that testimony might entail. Rather, appellant merely quoted the prosecutor, who said:
I told [trial counsel] that [Cooper and another] may give testimony to the effect that Tyrone Barnett was the shooter on the night of the offense.
Nor has he offered any basis for concluding that there is any possibility that Cooper could provide such testimony. Indeed, we do not even know that Cooper is even alive at this point. The absence of an affidavit or other credible proffer4 as to the allegedly exculpatory nature of Cooper’s testimony persuades us that the trial court did not err in declining to hold a hearing. See Sykes v. United States, 585 A.2d 1335,1338 (D.C.1991); see, e.g., Smith v. United States, 608 A.2d 129, 132 (D.C. 1992) (reversing denial without a hearing of motion alleging that counsel’s failures to adequately investigate location of incident, prepare defense, and examine witnesses resulted in presentation of uncorroborated defense where new counsel “proffered physical evidence regarding the location of the incident” and “proffered the statements of eleven witnesses, each of whom would have confirmed some portion of appellant’s version of the incident”); Wright v. United States, 608 A.2d 763, 766 (D.C. 1992) (reversing denial without hearing of motion alleging ineffectiveness where appellant asserted in affidavit facts supporting his claim); Rice v. United States, 580 A.2d 119, 121 (D.C.1990) (reversing denial without a hearing where allegation of ineffective assistance for failure to prepare alibi defense was supported by list of alibi witnesses who signed statements corroborating alibi and attesting that trial counsel never interviewed them); Ramsey v. United States, 569 A.2d 142, 149 (D.C.1990) (affidavit of witness raising material issue of fact considered significant factor in concluding that evidentiary hearing was required to resolve alleged factual dispute); see also 1 Criminal PractiCe Institute, Trial Manual 11.17 (1991) (“In order to obtain a hearing, it is advisable to substantiate the allegations of the motion by affidavits or other documents.”).
Put succinctly, we are not persuaded that the fact that evidence might be Brady material is sufficient to require a hearing in every case. Under the Brady rule, evidence in the possession of the government which is material and favorable to the accused must be disclosed. Brady v. Maryland, 373 U.S. 83, 87, 83 S.Ct. 1194, 1196, 10 L.Ed.2d 215 (1963). “[B]ecause the significance of an item of evidence can seldom be predicted accurately until the entire record is complete, the prudent prosecutor will resolve doubtful questions in favor of disclosure.” United States v. Agurs, 427 U.S. 97, 108, 96 S.Ct. 2392, 2399, 49 L.Ed.2d 342 (1976). Thus, after the record is complete, not all evidence identified by the government as Brady information will necessarily be material to the defense.
Moreover, the record does contain Cooper’s grand jury testimony. To the extent that it reflects what Cooper’s testimony may have been, it provides appellant no support; in fact, it undercuts his claim. The trial court reasoned that Cooper’s testimony at trial would have been either (1) consistent with his grand jury testimony and therefore not exculpatory, or (2) inconsistent with his grand jury testimony and therefore dubious, given that it would have been subject to impeachment.
Cooper told the grand jury that he saw “a whole lot of people” in the car, and that at the time he recognized only the driver and the individual who had been sitting in the back seat behind the passenger side *236before he got out of the car.5 When he got out of the car, “[h]e went under his coat, and everybody ran.” As Cooper ran, he heard gunshots.
With respect to the possibility that Cooper’s trial testimony would have been essentially the same as his grand jury testimony, we are persuaded by the trial court’s reasoning that if Cooper presented testimony consistent with what he told the grand jury, there is no reasonable probability that the result would have been different. Ready v. United States, 445 A.2d at 990 n. 16; see United States v. Frost, 502 A.2d 462, 464 (D.C.1985), cert. denied, 479 U.S. 836, 107 S.Ct. 134, 93 L.Ed.2d 77 (1986). As for the latter, the hypothetical possibility that Cooper’s trial testimony may have been different than that presented to the grand jury is an issue we do not reach for the reasons set forth above: appellant has offered no indication beyond sheer speculation that such would be the case. Thus, Cooper’s grand jury testimony only undercuts appellant’s already deficient showing that he is entitled to a hearing. See White v. United States, 484 A.2d 553, 558-89 (D.C.1984) (affirming denial of a hearing on claim of ineffective assistance of counsel where failure to prepare alibi defense, which was supported by an affidavit of the alibi witness, was too vague to support claim of ineffective assistance and contradicted appellant’s testimony at trial).6
Accordingly, the judgment of the trial court is
Affirmed.
. D.C.Code § 23-110 (1989).
. Ordinarily, a claim of ineffective assistance of counsel must be raised at the time of the direct appeal if the appellant "demonstrably knew or should have known of the grounds for alleging counsel's ineffectiveness.” Shepard v. United States, 533 A.2d 1278, 1280 (D.C.1987). Although the rule mandated by Shepard was applied prospectively and thus does not affect appellant's claim, we note that the absence of Cooper at trial, the basis of appellant’s allegation of ineffective assistance of counsel, was addressed in our opinion affirming his convictions. Yet, approximately nine years elapsed after we affirmed appellant’s convictions before he filed this motion alleging ineffective assistance of counsel.
. Brady v. Maryland, 373 U.S. 83, 83 S.Ct. 1194, 10 L.Ed.2d 215 (1963).
. See Gillis v. United States, 586 A.2d 726, 728 (D.C.1991) (defense counsel revealed at sentencing that witness not called at trial presented *236testimony at a preliminary hearing and resulted in dismissal of the charges).
. Although Cooper did not identify the individual in the back seat, there was testimony at trial that Tyrone Barnett got out of the car.
. Appellant also asserts that his trial counsel failed to properly prepare two witnesses for trial. His assertion is based primarily on the claim that their testimony was not as well presented as it could have been. We find this assertion vague and conclusory. Therefore, it did not require a hearing. See Pettaway v. United States, 390 A.2d 981, 984 (D.C.1978).