On April 5, 1977, Charles Ervin Williams was convicted for the armed robbery of a Louisville restaurant and the murder of one of its patrons, receiving the maximum life sentence for each crime.1 He now appeals, presenting four questions for our consideration. Of these, the only one which requires extensive discussion is whether the Commonwealth’s Attorney’s failure to provide the defense with information supportive of its claim that the prosecution obtained vacation of a conviction against its key witness in exchange for his testimony, deprived Charles of a fair trial. We believe that it did.
I
During the early morning hours of December 20, 1974, around 12:45, a dark-skinned man wearing a brightly colored ski *141mask and brandishing a 9mm automatic pistol entered Cooksey’s Grill in Louisville and commanded the manager and seven customers therein to lie face down on the floor. As Mike Morris rose from his chair to do so, the masked man shot him through the heart, killing him instantly. He then ordered Wanda Puckett, the manager, to open the cash register; after removing most of the money inside, he searched the pockets of both Morris and his tablemate, Barry Dorsey, and fled out the door. Two piles of loose change were later discovered in an alley behind Cooksey’s, one pile only 50 feet from the restaurant, the other behind a house at 1840 West Hill Street, just a few blocks from Charles’ residence at 2127 West Hill. The gun used in the robbery and murder was never found.
Because of the disguise which he had worn, none of the eyewitnesses were able to give a detailed description of the assailant when interviewed following the incident. All agreed that he was a brown-skinned male and that he was attired in a dark jacket and trousers. Delores Carter, who had obtained perhaps the best view of the masked man,2 said she was positive that he had blue eyes and estimated him to be 5 feet 5 inches in height. Other witnesses reported that he had gray or green eyes and guessed him to be from 5 feet 8 inches to 6 feet 2 inches tall. Charles has brown eyes and is exactly 6 feet in height.
Although he too had been unable on the morning of the 20th to identify the assailant, it later dawned on Barry Dorsey that the individual who had committed the crimes at Cooksey’s was one and the same person as a black male who had purchased cigarettes the evening of the 19th at the nearby gas station where Dorsey was employed. Approximately one week after this revelation struck him, Dorsey identified Charles from a group of police photographs as being that man. On December 29 Charles was asked, and he consented, to participate in a lineup before all of the witnesses to the robbery and murder. After viewing Charles and five other black males, first with and then without ski masks on, none of the other eyewitnesses recognized the assailant among the men. Dorsey again identified Charles; as a result, Charles was arrested later that afternoon.
While Dorsey’s identification of Charles was certainly important to the Commonwealth’s case, the key prosecution witness at trial, and the one around whose testimony the controversy in this case centers, was Myer Pettyjohn. Charles was originally tried on September 28,1976. At that trial, Pettyjohn initially testified that he knew absolutely nothing about the incident at Cooksey’s and that he had never seen Charles before in his life. After a brief recess during which time Pettyjohn conferred with an official from the state Department of Corrections, however, Petty-john recanted his previous statements and gave testimony incriminating Charles as the perpetrator of the robbery and murder at Cooksey’s.
According to this new testimony, on the morning of December 20, 1974, Pettyjohn had, despite the fact that he was on parole from a robbery conviction and was not supposed to be in Jefferson County, driven to Cooksey’s in search of his friend Mike Morris. While sitting in his car across from the restaurant, Pettyjohn heard a gunshot, then saw a black male run out of the building with a gun in one hand and a ski mask in the other. Although he had no idea at that time who the man was, on January 28,1975, Pettyjohn was placed in the Jefferson County jail after violating the conditions of his parole — he had been arrested in connection with yet another robbery — where he not only recognized Charles as the man he had seen at Cooksey’s, but was actually told by Charles that he had committed the crimes. When asked on cross-examination why he had changed his testimony after the *142recess, Pettyjohn responded that he had been afraid to testify against Charles until promised by the Corrections official that the two would be placed in different prisons if Charles should be convicted. Charles presented an alibi defense which was corroborated by several members of his family. Apparently unsure of whom or what to believe, the jury was unable to reach a verdict.
Charles was retried on April 5, 1977. Following a reiteration by Pettyjohn on direct examination of his “post-recess” testimony from the former trial, a Cotton hearing3 was held to determine whether Pettyjohn had ever been convicted of any felonies which might reflect adversely on his credibility as a witness. There, Petty-john admitted that he had been convicted of robbery on three occasions, but stated that the most recent conviction had been vacated after Charles’ first trial and that the charge was again pending.4 Upon learning this, defense counsel asked the trial court if he could question Pettyjohn about the vacation and the circumstances surrounding it when they returned to the courtroom; reasoning that a conviction which has been vacated is no longer admissible for Cotton purposes, the trial court ruled that he could not. When the trial resumed, defense counsel did his best on cross-examination to discredit Pettyjohn’s testimony, pointing out the two earlier robbery convictions, exposing his “pre-recess” testimony from the prior trial, and, without mentioning the vacation, implying the existence of a deal with the prosecution:
Q. And you know about people trying to make deals, don’t you?
A. What kind of deals 'are you talking about?
Q. I’m talking about giving testimony against somebody for a little slack on these charges that you may have against you.
A. Ño, I don’t know—
Q. You haven’t heard anything about that?
A. What are you talking about, on TV, real life, or what?
Q. Real life.
A. I guess it happens.
Q. You came in that door didn’t you? You’re on the outside now.
On redirect examination by the Commonwealth’s Attorney, however, Pettyjohn categorically denied having ever received any promises of leniency in exchange for his testimony.
Some five weeks after Charles’ conviction, defense counsel filed a motion for new trial alleging (1) that he had since trial discovered evidence supportive of the defense’s contention that Pettyjohn had been promised favorable treatment in exchange for his testimony against Charles and therefore possessed a motive to lie; and (2) that the Commonwealth’s Attorney had failed to disclose this evidence as required by Brady v. Maryland, 373 U.S. 83, 83 S.Ct. 1194, 10 L.Ed.2d 215 (1963), and its progeny. At a hearing on the motion, it was revealed that while incarcerated following his arrest in January of 1975 for robbery, Pettyjohn had written several letters to his fiancee in which he referred to using his knowledge of the incident at Cooksey’s and other crimes as a “trick” for obtaining release from prison, and stated he would only divulge this information to the authorities if they would “help get the hold off.” When questioned about these remarks, Pettyjohn admitted he had hoped to gain his freedom by testifying against Charles, but again denied that any promises had actually been made or that his testimony had been fabricated. It was further revealed that when Pettyjohn’s robbery conviction was in fact vacated after Charles’ first trial, the order authorizing *143the vacation had been sent to the prosecutor in Charles’ case, Commonwealth’s Attorney Zollinger, for his approval, despite the fact that he was in no way involved in the prosecution of Pettyjohn. Zollinger admitted during the hearing he had recommended that the conviction be vacated, but like Pettyjohn denied the existence of a deal. On June 24,1977, the motion for new trial was denied. This appeal followed.
II
In determining whether the court below acted properly in denying Charles’ motion for new trial, United States v. Agurs, 427 U.S. 97, 96 S.Ct. 2392, 49 L.Ed.2d 342 (1976) requires that we distinguish between two types of cases, each involving the discovery after trial of exculpatory evidence known to the prosecution but unknown to, and for that reason not specifically requested by,5 the defense: those which might be called “perjury” cases, and those which might be called “discovery” cases. See United States v. Sutton, 542 F.2d 1239 (4th Cir. 1976).
The hallmark of a “perjury” case, perhaps the most obvious example of which is Giglio v. United States, 405 U.S. 150, 92 S.Ct. 763, 31 L.Ed.2d 104 (1975), is an allegation by the defense that the undisclosed evidence reveals the presence of perjured testimony in the government’s case. In Giglio, the key prosecution witness, himself a potential indictee, testified at trial that he had received no promises of non-prosecution in exchange for his testimony implicating the defendant; after trial, the government admitted that such a promise had been made. Noting that the testimony of that witness was so vital to the success of the government’s case that the issue of his reliability may well have been determinative of the defendant’s guilt or innocence, the court awarded the defendant a new trial.
A “discovery” case, on the other hand, involves the suppression of evidence which is favorable in some other way to the defense: it is characterized not by a conviction based on false evidence, but rather by a conviction based merely on less than all the available exculpatory evidence. This evidence can be either directly exculpatory, as in Agurs itself, where the government withheld evidence supportive of the defendant’s claim of self-defense, or indirectly exculpatory, again in the sense that it impeaches the credibility of a witness whose testimony may be determinative of guilt or innocence. See Garrison v. Maggio, 540 F.2d 1271 (5th Cir. 1976) (Wisdom, J., dissenting); United States ex rel. Annunziato v. Manson, 425 F.Supp. 1272 (D.Conn. 1977). A case of the second type would, we suppose, have been created if defense counsel in Giglio had not elicited a denial from the witness that a promise had been made; for even in the absence of perjured testimony, evidence of a promise would still have been valuable to the accused to show that the witness possessed a motive to fabricate.6
Because the harm to the defendant resulting from nondisclosure in a “perjury” case is potentially twofold — not only does he not enjoy the advantage of being able to impugn the witness’ credibility, he actually suffers the disadvantage that the witness’ credibility is enhanced by the perjured testimony — in order to have his conviction set aside the defendant in such a case need only show that “the false testimony could in any reasonable likelihood have affected the judgment of the jury.” See Giglio, 405 U.S. at 154, 92 S.Ct. at 766, quoting from Napue v. Illinois, 360 U.S. 264, 79 S.Ct. 1173, 3 L.Ed.2d 1217 (1959). The defendant in a “discovery” case, however, who is harmed only in the former manner, must demonstrate that the newly discovered evidence, if it had been known to *144the jury, would have created á reasonable doubt as to guilt which would not otherwise have existed without the evidence. Agurs, 427 U.S. at 112, 96 S.Ct. 2392. This standard is both difficult for the defendant to meet, since it requires a greater showing of prejudice than does the “perjury” standard, and difficult for a reviewing court to apply, in that it requires a subjective appraisal of the evidence and its possible effect on the jury.
Obviously the threshold question in the instant situation is whether the undisclosed information, when considered in conjunction with other evidence in the case, adequately supports Charles’ allegation that the Commonwealth’s case contains perjured testimony so as to fit the case at hand into the “perjury” category. We believe that it does. For although the evidence of a deal in the present case is not as unequivocal as that in Giglio, so long as the evidence “even arguably give[s] rise to an inference of perjury,” Agurs, 427 U.S. at 114, 96 S.Ct. at 2402, it is sufficient to create a jury question on the matter, and the failure to disclose the information constitutes error. See Pyle v. Kansas, 317 U.S. 213, 63 S.Ct. 177, 87 L.Ed. 214 (1942); Mooney v. Holohan, 294 U.S. 103, 55 S.Ct. 340, 79 L.Ed. 791 (1935); of. Davis v. Alaska, 415 U.S. 308, 94 S.Ct. 1105, 39 L.Ed.2d 347 (1974). In the case at bar, the evidence supportive of Charles’ allegation that Pettyjohn expected prosecutorial aid in exchange for his testimony does appear, at least superficially, to contain the basic ingredients of a deal. Pri- or to Charles’ first trial, Pettyjohn stated in no uncertain terms that he would not testify against Charles unless guaranteed his release from prison. Pettyjohn then testified, and shortly thereafter was in fact released from jail. When embellished by the fact that Pettyjohn initially refused to incriminate Charles and did so only after conferring with a government official, and that the order vacating his conviction was sent to the prosecutor in Charles’ case for approval, despite his lack of connection with Pettyjohn’s case,7 we cannot discount altogether Charles’ allegation that the undisclosed evidence as it might have been developed by skilled counsel at trial would indeed have convinced the jurors that there was a deal.
This does not end our inquiry, however, since even if we assume for purposes of argument that the jury would have believed a promise was made and that Pettyjohn’s denial of such a promise was therefore false, it must still be determined whether there exists any reasonable likelihood that the false testimony could have affected the judgment of the jury under the evidence as a whole. Resolution of this question depends on at least two factors, including (1) the extent to which Pettyjohn was otherwise impeached, and (2) the importance of Pettyjohn’s testimony to the prosecution’s ease.
With respect to the first, we cannot say that any impeachment which might have resulted from disclosure of the suppressed information to the jury would have been merely cumulative. While it is true that defense counsel was able to cast some doubt on Pettyjohn’s believability anyway by exposing the fact that he was a convicted felon and that he had perjured himself at Charles’ prior trial, there is a vast difference between being able to show that a witness’ credibility is generally bad and that he has lied in the past, and being able to show that he has a specific motive to lie in the case at hand. See Davis and Annun-ziato, both supra. Had defense counsel known of the undisclosed evidence and presented it to the jury in such a manner as to convince them that Pettyjohn did in fact possess a motive to fabricate, therefore, this impeachment evidence might well have been the telling blow in discrediting his credibility.
*145Nor are we able to say that even if the jurors had heard the evidence, agreed there was a deal, and rejected Pettyjohn’s testimony entirely, they would nevertheless have convicted Charles anyway. Of all the evidence presented by the Commonwealth, Pettyjohn’s identification of Charles as the perpetrator of the robbery and murder at Cooksey’s was by far the most damaging. Pettyjohn was the only witness who claimed to have seen the assailant without his mask on. He was also the witness who alleged that Charles had confessed to the crimes. Had the jurors rejected his testimony, it is highly possible, perhaps even probable, that they, like their fellow jurors from the former trial, would have been unable to base a conviction on the remaining prosecution evidence. Because there is a reasonable likelihood that Pettyjohn’s testimony, and hence his reliability, may have been determinative of Charles’ guilt at trial, the failure by the prosecution to disclose evidence affecting his reliability requires that Charles be given a new trial.
Ill
It should be noted that the same result can be reached on the ground that Charles was denied the right “to be confronted with the witnesses against him” as. guaranteed by the Sixth and Fourteenth Amendments. As mentioned previously, it was discovered during the Cotton hearing at Charles’ second trial that the most recent of Petty-john’s robbery convictions had been vacated and that charges were again pending against him. Upon learning this fact, defense counsel asked the court if he might cross-examine Pettyjohn about the vacation and the circumstances surrounding it. The trial court, however, obviously thinking only of whether testimony relating to a vacated conviction was admissible for purposes of Cotton, ruled that counsel could not mention that conviction or anything relating to it.8
It is well established in this day and time that the right to cross-examine a witness to impeach his credibility or show motive or prejudice is fundamental to a fair trial. Davis, supra; Greene v. McElroy, 360 U.S. 474, 79 S.Ct. 1400, 3 L.Ed.2d 1377 (1959). Thus, a defendant has a right to expose the fact that a witness has criminal charges pending against him and thereby possesses a motive to lie in order to curry favorable treatment from the prosecution. See Annunziato, supra. In the instant case, Charles was denied that right because of the trial court’s ruling that the vacated conviction and the charges stemming from it were not proper subjects of cross-examination. Just as in Davis, counsel was prevented from making a record as to why Pettyjohn “might have been biased or otherwise lacked that degree of impartiality expected of a witness at trial.” Davis, 415 U.S. at 318, 94 S.Ct. at 1111. As a result, the jury was left to consider Pettyjohn’s testimony without any nonspeculative evidence as to what power the state could still exert over his freedom. Annunziato. Whether in every instance such a denial would amount to a “constitutional error of the first magnitude” requiring a new trial without any special showing of prejudice, cf. Davis, 415 U.S. at 318, 94 S.Ct. at 1111; and Smith v. Illinois, 390 U.S. 129, 88 S.Ct. 748, 19 L.Ed.2d 956 (1968), we need not decide. Suffice it to say that under the totality of circumstances existing in this case the court’s refusal to allow defense counsel to pursue the question of a possible *146“deal” through the process of a searching cross-examination was not consistent with our conception of fair trial, of which the right of confrontation and cross-examination is a vital part.
IV
Charles’ other three assignments of error require but brief comment:
First, we cannot say as a matter of law that Pettyjohn’s testimony incriminating Charles was perjured merely because it contradicted the testimony given by him prior to the recess at the first trial. The fact of the matter is that just as in most eases involving the recantation, after trial, of testimony given during trial, we simply do not know and have no way of knowing which story is correct and which story is false.
Secondly, while it is clear, in light of the trial court’s pretrial order that all prosecution witnesses be instructed not to mention it, that the testimony about Charles’ having been seen smoking marijuana should not have occurred, we do not believe that it could have significantly affected the judgment of the jury.
Finally, we similarly do not believe that Charles was unduly prejudiced by anything which occurred during closing argument. Although the comments by the prosecutor implying that witnesses in the case had been threatened by members of Charles’ family were improper, see Campbell v. Commonwealth, Ky., 564 S.W.2d 528 (decided February 21, 1978), they were not sufficient to deprive Charles of a fair trial.
The judgment is reversed and the case is remanded for a new trial.
PALMORE, C. J., and LUKOWSKY and REED, JJ., concur. JONES, STEPHENSON and STERN-BERG, JJ., dissent.. Although both the provisions under which Charles was indicted, 1966 Ky. Acts, Ch. 48, § 1 (KRS 433.140) and Ky.Stats. § 1149 (KRS 435.-010), originally permitted imposition of the death penalty, those sections of the statutes authorizing such punishment were subsequently declared unconstitutional. See, e. g., Caine v. Commonwealth, Ky., 491 S.W.2d 824, cert, denied 414 U.S. 876, 94 S.Ct. 80, 38 L.Ed.2d 121 (1973). Just twelve days after the commission of the offenses herein, both statutes were repealed. See 1974 Ky. Acts, Ch. 406, § 336 at p. 889; for current versions, see KRS 515.020 and KRS 507.020.
. In the confusion of the moment, Miss Carter had apparently stood up rather than lying down as ordered. This prompted the assailant, after he had shot Morris, to move to within one foot of Miss Carter, where he stared directly at her for several seconds and then told her she had better lie down on the floor or he would shoot her too.
. See Cotton v. Commonwealth, Ky., 454 S.W.2d 698 (1970).
. Pettyjohn was convicted and sentenced to 9 years’ imprisonment following the entry of a guilty plea on September 29, 1975, nearly four months after he had disclosed his information to the authorities. On January 31, 1977, he filed a motion pursuant to RCr 11.42 to set aside the guilty plea on the ground that he had been emotionally upset at the time the plea was entered. On February 21, 1977, the motion was granted.
. Where a specific request is made for information prior to trial, as in Brady, so long as there is a “substantial basis” for claiming materiality exists, “the failure to make any response is seldom, if ever, excusable.” Agurs, 427 U.S. at 106, 96 S.Ct. at 2399.
. But see Mr. Justice Marshall’s dissenting opinion in Agurs to the effect that the result in Giglio, and the standard for awarding a new trial which was utilized therein, would have been no different if perjury had not been involved. Id., 427 U.S. at 121, 96 S.Ct. 2392.
. Although it might be argued that the order vacating Pettyjohn’s conviction contained nothing which would indicate an expectation of favorable treatment — indeed, Commonwealth’s Attorney Zollinger was careful to note on the document that he had “never talked to this man but he testified on behalf of the Commonwealth without promise or agreement” — the mere fact that the order was sent to Zollinger for his approval is somewhat suspicious in and of itself. Cf. United States v. McCrane, 547 F.2d 204 (3rd Cir. 1976).
. MR. RECEVEUR: . . . he had a PV and then he was arrested for robbery while he was on parole.
MR. ZOLLINGER: That was set aside, wasn’t it?
A. Yes, sir.
MR. RECEVEUR: Is it pending?
A. Yeah.
COURT: Now wait a minute. You have been convicted previous to that of robbery also, which was not set aside, is that right?
A. Yes, sir.
COURT: So I think the limiting feature of the thing is quite applicable now and you should not ask him how many times or anything like that because after all, you’ve got a judgment set aside, I can’t presume that he’s
MR. RECEVEUR: Can I inquire of him if he knows why it was set aside or what ground?
COURT: No, sir. . . .