SCHWELB, Associate Judge:
On February 16, 1999, following a bench trial, Wayne Lanton was found guilty of assaulting his wife, Nnennaya Oti Lanton. He received a suspended sentence of imprisonment and was placed on probation. On August 18, 1999, Lanton filed a motion to vacate his sentence pursuant to D.C.Code § 23-110 (1998), alleging ineffective assistance of counsel. On March 22, 2000, the trial judge issued a written order in which she denied Lanton’s motion without a hearing. Lanton’s appeals from his conviction (No. 99-CM-245) and from the order denying his post-trial motion (No. OO-CO-487) were consolidated by order of this court. We conclude that the trial judge erred in denying Lanton’s § 23-110 motion without a hearing.
I.
This case arose from a domestic dispute between Lanton and his wife which occurred on July 30, 1998 at the home that the couple shared with their two young children, aged five and two. When Mrs. Lanton arrived at home early that afternoon, it appeared that her husband was attempting to clean up the apartment. In doing so, Mr. Lanton was apparently disposing of some old furniture and clothing. Mrs. Lanton became concerned that Mr. Lanton was throwing away clothes that still fit the children, including, in particular, some shoes that belonged to the Lan-tons’ daughter. According to Mrs. Lan-ton, her husband ridiculed her concerns.
It is undisputed that Mrs. Lanton began yelling at her husband, pointing out forcefully that he had not paid for the shoes and that he had no right to throw them away. The two principals’ accounts diverge as to exactly what happened after Mrs. Lanton began berating her spouse.
According to Mrs. Lanton, her husband told her to “get out of his face” and warned that, if she did not, he was going to “smack” her. Although Mrs. Lanton was much shorter and lighter than her husband,1 she apparently gave as good as she got; she testified that when she did not “get out of [Mr. Lanton’s] face,” her husband responded by striking his wife in her face. Mrs. Lanton admitted that she hit her husband back and that she continued to yell at him. According to the wife’s account, Mr. Lanton threatened to hurt her and
[898]*898the argument started a little louder, so he smacked me again. So I hit him back. And he told me to back off or he [was] going to throw me out a window. So I told him to go ahead and throw me out the window.
Mrs. Lanton claimed that her husband then “smacked me again and punched me and kicked me a lot,” but that she continued to hit him back because, in her words, she “wasn’t going to let him kick me or punch me around. So he left.” Mrs. Lan-ton testified that she locked her husband out and refused to let him in, but Mr. Lanton managed to kick the door open, bragging that he was a “mighty man.” When Mr. Lanton went into the kitchen to try to cook some food, Mrs. Lanton insisted that her husband “can’t cook that food because that’s my food, I just bought it.”
On the key question regarding who was the initial aggressor, Mrs. Lanton insisted that it was her husband who struck the first blow.2 She testified that she suffered “a little bit of [a] bruise” which she showed to an officer when the police arrived a short time later.3 The officers arrested Mr. Lanton but not his wife.
Mr. Lanton testified that he was cleaning the apartment when his wife asked him about the location of their daughter’s missing shoes. According to Mr. Lanton, his wife was “pissed” that he had seemingly thrown the shoes away, and she began to yell at him, tried to throw out his books, and generally became very aggressive. Mr. Lanton testified that he left the apartment to “chill out” in the hallway, but that his wife followed him and continued to scream at him and berate him. Mr. Lan-ton eventually returned to the apartment to cook some food, but his wife, who was still in a rage, insisted that it was her food because she had paid for it.4 According to Lanton, his wife punched him in the face, continued to yell at him, and tried to beat him. Mr. Lanton denied striking his wife, and he insisted that, throughout the entire episode, he simply attempted to protect himself and to ward off his wife’s blows. According to Mr. Lanton, his wife was the aggressor and initiated the physical confrontation. Lanton indicated that he was trained in martial arts, and he implied that if he had wanted to fight his wife, she would have got by far the worst of it.
The trial judge found Mr. Lanton guilty of assault. She found the wife to be a more credible witness than her husband, and noted that the wife had a far better recollection of what occurred. The judge continued:
I also find telling the difference in admitting of wrongdoing. To hear the Defendant tell it, he did everything right this day; he was just the picture of calm, intervening only to prevent the complaining witness from becoming out of control. Whereas, Mrs. Lanton admitted to her own wrongdoing but also was quite clear that she did not engage in any physical misconduct, which is what this case is about.
[899]*899I will also say that I found the Defendant to be a very arrogant man as he testified. And, again, the very poor memory that he has of what happened on this day, I just find it not credible.
II.
On August 20, 1999, Lanton filed a motion pursuant to D.C.Code § 23-110 in which he claimed that his trial counsel was constitutionally ineffective. Lanton alleged, inter alia, that his attorney
1. failed to adequately confer with Lan-ton prior to trial;
2. neglected to interview favorable witnesses whose names Mr. Lanton claimed to have provided counsel; and
3. conducted an inadequate cross-examination of Mrs. Lanton.
Attached to Lanton’s motion were letters from two of his neighbors, Santos Manuel and Daiv Johnson. Manuel’s letter, which was framed as a kind of informal affidavit, reads as follows:
TO WHOM OF THE COURT IT MAY CONCERN
June 9,1999
I Santos Manuel, am certifying that I have known Mr. Lanton for 3-4 months. We used to stay in the same building and next door to each other. I also certify that I saw Mr. Lanton leaving his apartment and I heard him saying “stop, stop, don’t use violence, what is wrong?” I saw, with my own eyes, in that same event, his wife beating him, Mr. Lanton, and I heard her cursing and insulting him. In fact, I heard Mr. Lanton’s wife saying “I will make you arrested, why don’t you beat me back?” His wife continued with violence even though Mr. Lanton was already in the hallway across to my apartment. I did not see Mr. Lanton raise his hand and beat his wife back.
Mr. Lanton is a caring and family person. I have been seeing him taking his kids to school and sometimes to parks.
I swear hereby that this information was written and given by me to the best of my knowledge.
Santos Manuel.
Mr. Johnson wrote that he lived next door to the Lantons, that the walls between the two apartments are thin, and that he “could not help overhearing what was going on.” According to Mr. Johnson, the wife
was clearly the aggressor and baiting him to fight her. [Mr. Lanton] responded by going out and sitting in the hall, in the hope [that] she would cool down.... It struck me as decidedly unjust that [the police] should have arrested him....
On November 16, 1999, the government filed its opposition to Mr. Lanton’s motion, together with an affidavit by Lanton’s trial attorney. The attorney stated in his affidavit that he had met with his client five times prior to trial, that he had tried unsuccessfully to reach Lanton on several other occasions, and that Lanton had never told him that there were any witnesses to the incident. The affidavit does not disclose whether counsel asked Lanton about possible witnesses, or whether he made any independent effort to determine whether neighbors or others in the area may have seen or heard any part of this obviously extended and noisy confrontation.5
On March 22, 2000, the trial judge issued a 7 page written order in which she denied Lanton’s § 23-110 motion without a [900]*900hearing. Noting that the allegations in Lanton’s motion were not made under oath, the judge “credited” trial counsel’s account that he had conferred with his client on several occasions and that Lanton had not furnished him with the names of favorable witnesses prior to the day of trial. The judge made this credibility determination notwithstanding the fact that counsel’s account had not been subjected to cross-examination, which is “the principal means by which the believability of a witness and the truth of his testimony are tested.” Davis v. Alaska, 415 U.S. 308, 316, 94 S.Ct. 1105, 39 L.Ed.2d 347 (1974); see also Tyree v. Evans, 728 A.2d 101, 103 (D.C.1999). The judge made no finding as to whether counsel had asked Lanton about possible witnesses or whether the attorney had conducted an investigation on his own initiative. With respect to the proffered testimony of Lanton’s two neighbors, the judge found that in one respect, Mr. Manuel’s statement contradicted Mr. Lanton’s trial testimony,6 and that “there is no indication that [Daiv Johnson] witnessed any physical abuse by either the defendant or the complainant.” Rejecting a number of other contentions raised in Mr. Lanton’s § 23-110 motion,7 the judge concluded:
The defendant’s final argument is that defense counsel failed to impeach the credibility of the complainant with information he could have obtained from discussions with, and subpoenas of, the defendant’s neighbor witnesses. The defendant asserts that such actions would have bolstered the credibility of the defendant and diminished that of the complainant in the eyes of the court. But the statements of the two neighbor witnesses, as discussed above, would not have been particularly relevant since they were not present and did not see the assault in question. The complainant admitted to yelling loudly at the defendant and this was not an issue. The Court cannot conclude that defense counsel’s cross-examination of the complainant was ineffective.
Based upon the pleadings and affidavits presented for the Court’s consideration, the Court credits the sworn testimony of defense counsel which disputed every significant claim of ineffective assistance of counsel that is raised in the defense motion, a motion that is unaccompanied by any sworn affidavit of the defendant himself. The Court further concludes that even had the information provided in the sworn affidavits of the two neighbor witnesses been presented at trial it would not have affected the trial’s outcome since it would not have altered the Court’s assessment of the complainant and the defendant’s credibility. Since it is clear from the pleadings and from the Court’s review of its own files and notes that the defendant is not entitled to the relief he is seeking, no hearing will be conducted on his motion.
These consolidated appeals followed.
III.
Section 23-110(c) provides in pertinent part as follows:
Unless the motion and files and records of the case conclusively show that the prisoner is entitled to no relief, the court shall cause notice thereof to be served upon the prosecuting [901]*901authority, grant a prompt hearing thereon, determine the issues, and make findings of fact and conclusions of law with respect thereto.
“In light of the foregoing provision, there is a presumption that a trial court presented with a § 23-110 motion alleging the ineffective assistance of counsel should conduct a hearing.” Dobson v. United States, 711 A.2d 78, 83 (D.C.1998) (citations omitted). In order to uphold the denial of a § 23-110 motion without a hearing, we must be satisfied that “under no circumstances could the petitioner establish facts warranting relief.” Ramsey v. United States, 569 A.2d 142, 147 (D.C.1990) (quoting Fontaine v. United States, 411 U.S. 213, 215, 93 S.Ct. 1461, 36 L.Ed.2d 169 (1973)). The determination whether or not to hold a hearing is discretionary, see, e.g., Webster v. United States, 623 A.2d 1198, 1206 (D.C.1993), but “because § 23-110 is a remedy of virtually last resort, any [non-frivolous] question whether a hearing is appropriate should be resolved in the affirmative.” Gibson v. United States, 388 A.2d 1214, 1216 (D.C.1978) (per curiam).
This court has recognized three categories of claims that do not merit a hearing:
(1) vague and conclusory allegations;
(2) palpably incredible claims; and
(3) assertions that would not merit relief even if true.
Dobson, supra, 711 A.2d at 83 (citation omitted). Lanton’s claims in his § 23-110 motion are not vague or conclusory, nor can they be characterized as “palpably incredible.” The question to be decided is whether, if true, they would merit relief.
The standards which govern claims of ineffective assistance of counsel have been articulated by the Supreme Court in Strickland v. Washington, 466 U.S. 668, 687, 104 S.Ct. 2052, 80 L.Ed.2d 674 (1984):
First, the defendant must show that counsel’s performance was deficient.... Second, the defendant must show that the deficient performance prejudiced the defense. This requires showing that counsel’s errors were so serious as to deprive the defendant of a fair trial, a trial whose result is reliable.
“The failure to make a proper pretrial investigation, to interview exculpatory witnesses, and to present their testimony constitutes constitutional ineffectiveness.” Byrd v. United States, 614 A.2d 25, 30 (D.C.1992) (citations omitted). If the existence, identity or location of a potential exculpatory witness is unknown, counsel is required to make all reasonable inquiries, and to take any other appropriate steps, to find and interview such a witness. See, e.g., Frederick v. United States, 741 A.2d 427, 438-39 (D.C.1999).
In the present case, the principal issue on which Lanton’s guilt or innocence turned was whether he or his wife was the aggressor. This is so because the wife made no secret of the fact that, notwithstanding her husband’s far greater height and weight, she did some punching and pummeling of her own; she justified her conduct upon the grounds of self-defense following an assault upon her by her husband. The judge heard only two witnesses on this issue, namely, the two protagonists. The judge credited the wife and not the husband.
But a careful consideration of the statements of the two neighbors reveals that both of them proffered information that went to the heart of the question whether it was the husband or the wife that committed the initial assault. According to Mr. Manuel, Mrs. Lanton, after beating on her husband, asked him (tauntingly) “why don’t you beat me back? ” (Emphasis added.) Mr. Johnson similarly alleged that the wife “was clearly the aggressor and [902]*902baiting him to fight her.” (Emphasis added.)8 If the proffered testimony of the two neighbors was true — and, for purposes of whether Lanton was entitled to a hearing, we must assume that it was true, as the judge was in no position to discredit the witnesses without giving them an opportunity to testify — then it surely casts grave doubt on Mrs. Lanton’s allegation that the husband was the aggressor. If Mr. Lanton had been assaulting his wife, she would hardly have taunted him for not fighting back! Yet in stating that the testimony of the two neighbors would not have affected the outcome of the trial, the judge did not focus at all on the allegations that the wife taunted the husband for not fighting her.9
Moreover, if Lanton’s attorney had been aware of the statements of the two neighbors, his cross-examination of Mrs. Lanton could have been far more effective. For example, counsel could have asked the wife if she had mocked her much larger husband for his unwillingness to fight her. An affirmative answer would have cast doubt on her claim that she was the victim of an assault by her husband. If, on the other hand, the wife had denied taunting her husband, her account — and she was the only prosecution witness — would have been in conflict with the testimony of the two neighbors.
IV.
The government takes the position that because Lanton filed no sworn affidavit in response to the affidavit of his trial counsel, the allegations in Lanton’s § 23-110 motion lack sufficient substantiation. We do not agree.
It is true that, where a defendant claims in a post-trial motion that his counsel was ineffective by failing to call prospective witnesses, we have required “an affidavit or other credible proffer as to the allegedly exculpatory nature of [the prospective witnesses’] testimony.” Ready v. United States, 620 A.2d 233, 235 (D.C.1993). In Sykes v. United States, 585 A.2d 1335 (D.C.1991), for example, the defendant, who had been convicted of selling heroin to an undercover police officer, claimed that his trial attorney was constitutionally ineffective. The attorney had not called as a witness, or even interviewed, one Audrey Smith, who had been present on the scene of the undercover buy. According to Sykes’ affidavit, Ms. Smith “would have been able to corroborate my testimony, and establish my innocence of the charges against me.” Under the particular circumstances of the case, however, it appeared likely that if Ms. Smith had testified as Sykes hoped that she would, she would have incriminated herself in connection with the transaction that led to Sykes’ conviction. The trial judge therefore found it likely that, if Ms. Smith had been called as a witness, she would either have invoked her privilege against self-incrimination or provided testimony unfavorable to Sykes. The judge concluded that the defense could not satisfy Strickland’s prejudice prong, and denied Sykes’ § 23-110 motion without a hearing.
[903]*903On appeal, this court stated that “it would have been judicious on the part of [Sykes’ attorney] at least to attempt to obtain Ms. Smith’s version.” Id. at 1337. Indeed, it would have “behooved” counsel to interview any witness who might have knowledge of the crime. Id. at 1338. But
Ms. Smith ... was no ordinary witness. The possibility that she would have “confessed” to the serious crime of distribution of heroin, and would have thereby voluntarily made herself vulnerable to the possibility of prosecution, conviction, and incarceration, was surely remote. On the other hand, the likelihood that upon being interviewed Ms. Smith would have denied having been the perpetrator of the charged offenses (either falsely, as Sykes contends, or truthfully, as the government maintains), or would have invoked her constitutional privilege against self-incrimination, was substantial.
Id. The court stated that even under these circumstances, “it might well have been wise” for the trial judge to hold a hearing on Sykes’ § 23-110 motion. Id. at 1340. Nevertheless, the court concluded that
on these particular facts, where Sykes failed to produce an affidavit from Ms. Smith, where Ms. Smith would have had to risk incriminating herself to assist Sykes, and where the defense case depends on a jury’s crediting that Ms. Smith sold drugs to Officer Awkard after being warned by Sykes that Awkard was a policeman, the trial judge acted within her discretion in concluding that a hearing could serve no useful purpose.
(Footnote omitted.) In a dissenting opinion, Judge Mack indicated that she would have remanded the case for a hearing on Sykes’ § 23-110 motion.
The court’s recognition that Sykes was a close case lends support to Lanton’s claim that, on this record, he was entitled to a hearing on his motion. In Sykes, the circumstances made it highly improbable that Ms. Smith would provide testimony favorable to the defendant when this would have required her to incriminate herself, and the court concluded-somewhat reluctantly-that no hearing was required if Sykes was unable to produce an affidavit from Ms. Smith. Here, on the other hand, the defense proffered the testimony of the two neighbors with its motion, and there was no reason to doubt their willingness to testify. Although conventional sworn affidavits would have been preferable, it would surely exalt form over substance to deny a hearing simply because the statements were not notarized, especially when, as we have noted, “ § 23-110 is a remedy of virtual last resort.” Gibson, supra, 388 A.2d at 1216. Indeed, the signed statements of the neighbors, one of which was framed in quasi-affidavit form, surely qualified as “other credible proffer[s],” as that term was used by the court in Ready, supra, 620 A.2d at 236.
Although Lanton’s allegation that he gave his attorney the names of neighbor witnesses was unsworn, there were no circumstances here suggesting that Lanton would be unwilling to testify in his own behalf or to confirm, under oath, the allegations in his pleading. We therefore do not believe that, on this record, Lanton’s failure in this case to file a separate affidavit verifying the allegations in his motion should result in the denial of the motion, with prejudice,10 without a hearing. The [904]*904§ 23-110 motion was, after all, in the nature of a pleading, roughly comparable to a complaint in a civil action. A motion which raises issues regarding events outside the trial record should not be denied with prejudice because the defendant’s initial pleading as to his own dealings with his attorney, to which he hoped to testify at a hearing, was not submitted under oath. In this case, unlike in Sykes, it would have been most astonishing if Lanton had been unwilling to swear to the facts alleged in his motion.11
But even if we were to discount unsworn allegations in Lanton’s pleading and therefore treat trial counsel’s affidavit as unre-butted with regard to counsel’s discussions with his client, denial of Lanton’s motion without a hearing would arguably still have been unwarranted. It is the function of the attorney, not of the client, to prepare a case for trial. Assuming, arguendo, that Lanton did not adequately communicate to his lawyer that Santos Manuel and Daiv Johnson were potential defense witnesses, there is nothing in the record to suggest that counsel ever asked the client for any information about what the neighbors or other possible witnesses might know about the alleged offense. Moreover, this incident obviously caused a considerable hullabaloo, and local residents might reasonably be expected to have seen or heard some of what took place. In fact, one of the neighbors apparently called the police. Counsel’s affidavit did not indicate that he conducted any neighborhood investigation or undertook to obtain information from anyone other than Lanton himself. Even as to Lanton, the affidavit did not reveal what, if any, inquiries counsel posed.
It may be that, if a hearing had been held, trial counsel could have elaborated on the facts disclosed in his affidavit and established that his performance satisfied the standards established by Strickland and its progeny. Counsel would, however, have been subject to cross-examination by Lanton’s new attorney, and his testimony could have been more effectively evaluated. See Davis, supra, 415 U.S. at 316, 94 S.Ct. 1105. The trial judge would then have had a far more complete and reliable record on which to base her disposition of Lanton’s claims of deficient performance and prejudice.
V.
We conclude that Lanton has proffered sufficient evidence, both as to deficient performance and as to prejudice, to entitle him to a hearing on his § 23-110 motion. There is a reasonable probability that Lan-ton could establish at a hearing that his attorney knew, or should have known, of the potential testimony of Manuel and Johnson, and that counsel’s failure to present their testimony was unreasonable “under prevailing professional norms.” Strickland, supra, 466 U.S. at 688, 104 S.Ct. 2052. If true, the claim of each neighbor that the wife appeared to be the aggressor and that she mocked her husband for not fighting back was highly probative as to who assaulted whom. Moreover, as we have previously observed, knowledge of these allegations would have [905]*905enabled counsel to conduct a far more effective cross-examination of the defendant’s wife, who was the only prosecution witness.
There is likewise a reasonable probability that, if the two neighbors had testified in conformity with their proffers, and if the trier of fact had believed them, the outcome of the trial would have been different.
[T]he result of a proceeding can be rendered unreliable, and hence the proceeding itself unfair, even if the errors of counsel cannot be shown by a preponderance of the evidence to have determined the outcome.
Mack v. United States, 570 A.2d 777, 784 (D.C.1990) (quoting Strickland, supra, 466 U.S. at 694, 104 S.Ct. 2052). If Mrs. Lan-ton engaged in the particular taunting behavior that these witnesses described, it would have been substantially more difficult for the prosecution to prove, beyond a reasonable doubt, that Mr. Lanton assaulted his wife, rather than the other way around.
VI.
For the foregoing reasons, in No. 00-CO-487, the order denying Lanton’s § 23-110 motion without a hearing is reversed. The case is remanded to the trial court for further proceedings consistent with this opinion.
So ordered.
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