After a jury trial, appellant was convicted of armed robbery in violation of D.C. Code §§ 22-2901, -3202 (1981 & 1985 Supp.), and sentenced to an indeterminate term of imprisonment of six to eighteen years. On appeal, appellant claims that the trial judge erred in limiting cross-examination of a government witness, admitting testimony corroborating out-of-court identifications of appellant made by several complaining witnesses, refusing to limit the government’s use, for impeachment purposes, of appellant’s prior convictions, and limiting defense counsel’s closing argument. Finding these claims to be without merit, we affirm.
I
On March 13, 1982, shortly before 4:00 a.m., Forrest Jackson was standing near a bus stop located at the corner of 8th and H Streets, N.E., just in front of a Seven-Eleven convenience store. Michelle Brown and James Moore, along with several other individuals, were sitting on a bench inside the sheltered bus stop, and Charles Price and Charlene Bray were inside the Seven-Eleven store.
At approximately 4:00 a.m., appellant walked up to Jackson and asked him if he knew “where any marijuana was.” When Jackson responded negatively, appellant walked away. Jackson testified that he immediately recognized appellant, who was wearing a beige jacket and a blue shirt, because he had “seen him” on three or four prior occasions.
Several minutes later, another man, later identified as Leonard Briscoe walked up to Jackson and pointed a silver pistol at him. As Michelle Brown, James Moore, and Charles Price watched, appellant approached Jackson from behind, reached into his pants pocket, and removed his blue leather wallet. After Briscoe had searched Jackson’s wallet and belongings, he demanded that Jackson give him and appellant three gold chains that Jackson was wearing around his neck. Jackson refused and appellant punched him in the face. Jackson then broke free from the robbers and ran toward the nearby Seven-Eleven.
As Jackson ran toward the store, appellant ran down the street and away from the robbery scene. Leonard Briscoe then proceeded to rob Michelle Brown, James Moore, and Charlene Bray, who had returned to the bus stop from the Seven-Eleven as appellant ran away.
Meanwhile, Forrest Jackson and Charles Price had run into the Seven-Eleven and told Donald Bell, who was working behind the counter, about the robbery. Bell, an off-duty Metropolitan Police Officer, telephoned the police. After hearing a gunshot, Bell drew his service revolver and walked out of the Seven-Eleven toward the bus stop, where he saw Leonard Briscoe kneeling in front of Michelle Brown, James Moore, Charlene Bray and the other bus patrons. Bell ordered Briscoe to “freeze” but Briscoe turned toward him as if to fire his weapon. Bell then fired his service revolver, hitting Briscoe in the neck and Briscoe fled as the two men exchanged gunfire.
On G Street, between 7th and 8th, Leonard Briscoe fell against the rear portion of a light-colored, four-door, Chevrolet automobile parked in front of an alley. Bell noticed that there were two people inside the Chevrolet, one of whom helped Leonard Briscoe into the car. After Leonard Bris-coe entered, the Chevrolet drove away at a high rate of speed. Bell returned to the Seven-Eleven, and reported the description of the car to the police.
Police Officer Frederick Lewis heard a “lookout” for a four-door Chevrolet automobile occupied by three robbery suspects shortly after 4:00 a.m. Upon hearing the lookout, Lewis drove to Capitol Hill Hospi*516tal on 8th Street to see if anybody had been admitted with a gunshot wound. Upon arriving, Lewis found a four-door Chevrolet automobile parked in front of the entrance to the emergency room. Lewis noticed a large amount of blood on the rear seat and floorboard of the car and a trail of blood leading from the car to the emergency room entrance. As Lewis began to follow the trail of blood, two men — appellant and Maurice Briscoe, Leonard Briscoe’s brother and appellant’s codefendant — came out of the hospital at a “hurried pace.” After brief questioning, appellant and Maurice Briscoe were placed under arrest.
Police Officer Michael McGraw and Sergeant Charles Bailey of the Metropolitan Police Department arrived at Capitol Hill Hospital several minutes later. The officers found a beige jacket lying on the back seat of the Chevrolet. Inside the pocket of the jacket was Forrest Jackson’s blue leather wallet and a card that had been inside the wallet taken from Jackson. Also found in the car were Jackson’s blue duf-flebag, containing his clothing, toiletry items, and several photographs. A .32 caliber Smith and Wesson revolver was found in the middle of 8th Street, approximately two hundred feet from the hospital.2
Appellant and Maurice Briscoe were brought back to the scene of the robberies where a series of “show-up” identifications were conducted. None of the witnesses identified Maurice Briscoe. At the show-up, however, Forrest Jackson positively identified appellant as the man who had taken his wallet and punched him in the face. Michelle Brown and James Moore both stated that appellant “look[ed] like” one of the two men who had robbed Jackson, and Charlene Bray stated that appellant was the same height as the man who had run from the scene as she walked out of the Seven-Eleven. At trial, both Forrest Jackson and Charles Price positively identified appellant as the man in the beige jacket who, along with Leonard Briscoe, had robbed Jackson.
II
Appellant’s first claim on appeal is that his confrontation rights under the Sixth Amendment were violated by a ruling of the trial judge limiting cross-examination of Forrest Jackson on the issue of bias. We disagree.
During cross-examination of Forrest Jackson, appellant’s counsel asked Jackson if he ever smoked marijuana. Upon gaining an admission that he had, defense counsel then asked, “And it’s also a fact that on occasion you have also sold marijuana, isn’t that correct?” The prosecutor objected to the question, and at an ensuing bench conference, the court asked defense counsel to proffer a basis for the question. The following colloquy occurred:
DEFENSE COUNSEL: Your Honor, the good faith basis of that question is that Mr. Jones told me that Mr. Jackson has sold him marijuana on previous occasions and that that is a motive for why he is testifying. It is bias, Your Honor.
* # * * * *
THE COURT: How many occasions, what, what, why would such a transaction provide a motive? I mean, even assuming it was true, why would that make him biased?
DEFENSE COUNSEL: As I understand it, Your Honor, there was something that at one point in time, there was something wrong with one of the transactions. I think it was only one transaction. And Mr. Jackson was dissatisfied with it. The way I understand it from Mr. Jones. THE COURT: Well, you’re asking whether Mr. Jackson had sold it. That doesn’t — I mean he is not a dissatisfied purchaser if he is a seller.
DEFENSE COUNSEL: No, he was dissatisfied with the transaction, Your Hon- or.
*517Appellant claims that the trial judge erred in sustaining the prosecutor’s objection to this line of questioning.
The right to cross-examine the government’s witnesses is inherent in a defendant’s Sixth Amendment right of confrontation. Davis v. Alaska, 415 U.S. 308, 315-16, 94 S.Ct. 1105, 1109-10, 39 L.Ed.2d 347 (1974). While it is recognized that “[The] extent of cross-examination [of a witness] with respect to an appropriate subject of inquiry is within the sound discretion of the trial court,” Alford v. United States, 282 U.S. 687, 694, 51 S.Ct. 218, 220, 75 L.Ed.2d 624 (1931); see also In re C.B.N., 499 A.2d 1215, 1218 (D.C.1985); Flecker v. United States, 358 A.2d 322, 323 (D.C.), cert. denied, 429 U.S. 977, 97 S.Ct. 486, 50 L.Ed.2d 585 (1976); we have repeatedly stated that “bias is always a proper subject of cross-examination.” Springer v. United States, 388 A.2d 846, 855 (D.C.1978) (quoting Hyman v. United States, 342 A.2d 43, 44 (D.C.1975)); see also Villaroman v. United States, 87 U.S.App.D.C. 240, 241, 184 F.2d 261, 262 (1950) (bias of witness is “always relevant”); Tompkins v. United States, 236 A.2d 443, 445 (D.C.1967) (same). Still, cross-examination of a government witness on the subject of bias must proceed in accordance with established evidentiary rules of procedure. Cf. Chambers v. Mississippi, 410 U.S. 284, 302, 93 S.Ct. 1038, 1049, 35 L.Ed.2d 297 (1973). Thus, to survive objection, the questioner must proffer “some facts which support a genuine belief” that the witness is biased in the manner asserted. United States v. Fowler, 151 U.S.App. D.C. 79, 81, 465 F.2d 664, 666 (1972); see also Hazel v. United States, 319 A.2d 136, 140 (D.C.1974) (attorney may not ask questions of witness that are “totally groundless”). In addition, the attorney must proffer facts sufficient to permit the trial judge to evaluate whether the proposed question is probative of bias. See Best v. United States, 328 A.2d 378, 381-82 (D.C.1974); see also Hawkins v. United States, 461 A.2d 1025, 1034 (D.C.1983), cert. denied, 464 U.S. 1052, 104 S.Ct. 734, 79 L.Ed.2d 193 (1984); Flecker v. United States, supra, 358 A.2d at 324.
On appeal, appellant explains that the theory of bias he sought to pursue in his questioning of Forrest Jackson was that “Jackson wanted to retaliate against him for a drug transaction for which he was never paid.” In support, appellant notes that this court has recognized that a witness’ failure to be paid for drugs sold to a defendant is a potential source of witness bias. See Johnson v. United States, 418 A.2d 136, 141-42 (D.C.1980).
Appellant’s argument is unavailing, however, because his proffer was insufficient to permit the trial judge to evaluate whether the proposed line of questioning was probative of bias. Indeed, in his proffer, defense counsel never explained that Jackson had sold appellant marijuana for which he had not been paid. Rather, counsel only obliquely stated “that at one point, there was something wrong with one of the transactions. I think it was only one transaction. And Mr. Jackson was dissatisfied with it.” Defense counsel never proffered any facts explaining how or why Jackson was “dissatisfied” with the alleged transaction. Absent any explanation as to how the drug transaction may have resulted in bias on the part of Mr. Jackson, appellant’s claim that the trial judge abused his discretion in precluding this line of questioning fails.3
In reaching this conclusion, we recognize that “[a]n exhaustive proffer is not normally a strict requirement for initiation of a line of cross-examination.” Best v. United States, supra, 328 A.2d at 382; see also Moss v. United States, 368 A.2d 1131, 1135 n. 2 (D.C.1977). Nevertheless, we observe that proffers found sufficient in other cases are more ample than that present*518ed here. In Best v. United States, supra, 328 A.2d at 382, for example, the defendant wanted to cross-examine his arresting officer on alleged bias resulting from an altercation following his arrest. The court questioned the relevancy of the line of questioning, and invited a proffer to explain its purpose. The proffer was as follows:
Your honor, on the day of the incident this officer struck Mr. Best and put him in the hospital and he was taken to the hospital that evening. There is evidence of police brutality and it is admissible to show bias on the part of the police officer. ... It’s perfectly admissible to show bias.
Id. at 380. After erroneously concluding that an altercation following the defendant’s arrest and search could not be relevant to bias, the trial judge precluded the line of questioning. On appeal, we reversed, finding the trial judge’s conclusion to be error as a matter of law, and the proffer sufficient.
Best is distinguishable, in our view, because the proffer in that case was specific as to who was involved, what transpired, and when and where the events resulting in bias occurred. Moreover, the nature of the incident — an alleged beating — was clearly probative of the issue of bias. By contrast, the proffer in this case was specific only as to who was involved. The description of what transpired — a drug transaction over which there was dissatisfaction — was manifestly vague. In addition, no explanation was offered as to when the alleged drug transaction occurred. Indeed, counsel should have been able to explain to the court how the proposed line of inquiry was relevant to bias, and should have been able to find out more about the matter from his client. Finally, the interaction described — a drug transaction in which appellant was the buyer — could reasonably be viewed as less probative of bias than the police brutality alleged in Best. Thus, we find no support in Best, supra, for appellant’s claim that the proffer in this case was adequate.4 See also Smith v. United States, 389 A.2d 1364, 1368 (D.C.1978) (court erred in restricting cross-examination of government witness where proffer clearly indicated that the witness was a government informant).
Ill
At trial, Detective Joseph Kacklik recounted the out-of-court identifications of appellant made by several witnesses immediately after the robbery.5 On appeal, appellant claims that Detective Kacklik’s testimony constitutes inadmissible hearsay because several of the identifications recounted by him at trial were not definitive. We disagree.
It is well established that “extrajudicial identification testimony is admissible as independent substantive evidence of identity as long as the out-of-court declar-ant is available for cross-examination at trial.” Harley v. United States, 471 A.2d 1013, 1015 (D.C.1984); see Warren v. United States, 436 A.2d 821, 837 (D.C.1981); Morris v. United States, 389 A.2d 1346, 1350 (D.C.1978). This court has approved the “admission of a victim’s pretrial description of a defendant through the ... testimony of a police officer,” Harley v. United States, supra, 471 A.2d at 1015, and has not required that the out-of-court declarant be absolutely certain of his extrajudicial identification in order for the testimony to be admitted. See id. at 1015-16 *519(testimony that pistol shown to witness at scene of robbery “was similar in size, shape and color” to the gun used by the robber properly admitted). Moreover, we have made it clear that out-of-court identification testimony is admissible even when the witness is unable to make an in-court identification. Rice v. United States, 437 A.2d 582, 583 (D.C.1981) (per curiam).
In this case, all of the out-of-court declarants whose “show-up” identifications were recounted by Detective Kacklik testified at trial. Consequently, Detective Kacklik’s extrajudicial identification testimony was properly admitted as independent substantive evidence of appellant’s identity. Appellant’s claim that this evidence constituted inadmissible hearsay is, therefore, without merit.
IV
Next, appellant argues that in permitting the prosecutor to impeach him with a prior conviction for unlawful possession of a prohibited weapon, the trial judge abused his discretion by allowing the government to specify that the earlier charge involved a gun. Again, we disagree.
D.C.Code § 14-305(b)(2) (1981), sanctions the use of a defendant’s prior convictions for impeachment purposes at trial. We have made it clear that under this provision, when a defendant takes the stand, the court “must permit the prosecutor to attack his or her credibility by introducing recent prior convictions for felonies and other crimes involving dishonesty or false statement.” Hill v. United States, 434 A.2d 422, 429 (D.C.1981), cert. denied, 454 U.S. 1151, 102 S.Ct. 1020, 71 L.Ed.2d 307 (1982). Moreover, control over the proper scope of witness examination is committed to the sound discretion of the trial court. See Middleton v. United States, 401 A.2d 109, 126 (D.C.1979).
Here, the prosecutor, at a colloquy during the government’s case, indicated that he intended to use a 1979 conviction for possession of a prohibited weapon to impeach appellant’s credibility if he testified in his own defense. The prosecutor further stated the government’s intention “to use the term ‘gun’ when it asks him about those prior convictions ... as opposed to just merely mentioning possession of a prohibited weapon.” While conceding that the conviction could be used for impeachment purposes, appellant maintains that the prejudicial impact from mention of the gun outweighed its probative value. Appellant asserts on appeal that the error was reversible because it influenced his decision not to testify. In light of the clear statutory language authorizing the use of prior convictions for impeachment purposes, however, and the trial judge’s broad authority to control the scope of cross-examination, we find no abuse of discretion in the court’s ruling.6
y
Finally, appellant argues that the trial court erred when it ruled, during defense counsel’s closing argument, that certain of counsel’s comments made in summation were “totally outside of the range of anything for the jury to consider.” This claim is without merit.
We have repeatedly stated that counsel may not express their personal beliefs or opinions about the existence or non-existence of a particular fact or otherwise “testify” to the jury in summation. See Villacres v. United States, 357 A.2d 423, 426-28 (D.C.1976); United States v. Bell, 165 U.S.App.D.C. 146, 164-65, 506 F.2d 207, 225-26 (1974). In this case, defense counsel attempted, in his closing argument, to discredit the testimony of Charles Price by arguing that his testimony had been orchestrated by Forrest Jackson, another government witness:
*520As for Mr. Price, when you’re considering his testimony, keep in mind that Mr. Price when he first talked to the police, when the incident was fresh in his mind, and the police were asking him questions about what he saw, did not tell the police that his good friend Forrest Jackson had been robbed. He left that out. He did not tell the police that he recognized the man who they had brought back, and then who was being accused, he knew quite well that he was being accused of robbing his friend Forrest Jackson.
Now, I ask you, ladies and gentlemen of the jury, does that make sense? Of course, it doesn’t. It would make sense that [if] a friend [ ] wants to help him, he is going to try to tell the police everything he saw regarding his friend first, then anything else that happened. But he starts with the robbery of the gunman by his — himself with the girl.
What actually happened, ladies and gentlemen, was Mr. Price was down at the scene nearby, saw the subsequent occurrences, did not see Mr. Jackson get robbed, as he described [it] in this statement to the police. And then later on Mr. Jackson came to him and said, didn’t you see me get robbed, you must have seen me get robbed. [Emphasis added.]
Significantly, no evidence had been introduced suggesting that Price had not seen the robbery or that Jackson had suggested the robbery to him. Given this state of the record, the court could reasonably perceive defense counsel, at least in part, as attempting to testify to the jury as to facts not in evidence. Consequently, the trial court did not abuse its discretion in interrupting this portion of closing argument, and instructing the jury to disregard it. Accordingly, the conviction on appeal is
Affirmed.
. At trial, Forrest Jackson and James Moore identified the revolver as being similar in appearance to the pistol that Leonard Briscoe had used during the robberies.
. Defense counsel could, of course, have requested a brief recess to obtain further information from his client on the nature of the bias resulting from the drug transaction with witness Jackson.
. Through our analysis of Best v. United States, supra, we do not intend to suggest that counsel is required to specify "who, what, and when” in all proffers of bias. Rather, we attempt only to articulate the basis for our view that the proffer found adequate in Best v. United States, supra, was more ample than that presented for review here.
. Detective Kacklik testified that Forrest Jackson positively identified appellant as the man who took his wallet, that Michelle Brown and James Moore both identified appellant as “looking like" one of the robbers, and that Charlene Bray indicated that appellant was the same height as the man she had seen run from the scene of the robbery.
. See abo Luce v. United States, 469 U.S. 38, 105 S.Ct. 460, 83 L.Ed.2d 443 (1984) (under Fed.R. Evid. 609(a), in order "to raise and preserve for review the claim of improper impeachment with a prior conviction, a defendant must testify”).