OPINION
NIX, Chief Justice.In this appeal, the Commonwealth presents two issues for our review: first, whether the Superior Court erred in concluding that a claim of prosecutorial vindictiveness should have been presented to the jury; and second, whether the Superior Court erred in determining that appellee should have been given the opportunity to cross-examine an adverse witness for bias. For the following reasons, we affirm the order of the Superior Court.
The circumstances predicating this appeal are as follows. Janet Butler was acquitted by a jury of prostitution charges in March, 1984. During the trial, while testifying in her own behalf, she was asked by her attorney if she had ever been convicted of a crime. She responded, “No, sir.” The prosecutor’s objection to this testimony was overruled, and Ms. Butler was permitted to repeat her answer. After she was acquitted, Ms. Butler filed a civil suit against Police Detective Dennis O’Leary and several other Delaware County officials based upon an allegedly coercive body cavity search.1 Shortly thereafter, the county authorities discovered that Ms. Butler did have a prior conviction for prostitution in the state of Delaware, and that she was also *10in violation of her probation. She subsequently was transferred to Delaware County to face charges of perjury and false swearing based upon her testimony at the prostitution trial.
Ms. Butler contended that the perjury charges were brought in retaliation for her civil suit. During a pre-trial conference before the perjury prosecution, defense counsel presented to the trial judge the theory of prosecutorial vindictiveness. Prior to opening argument, the judge informed counsel that he would not permit any reference to the Commonwealth’s motive for bringing the peijury charge. The court stated that it did not consider the Commonwealth’s motive to be an issue in the case, and that it would not permit any evidence of the pending civil suit to be presented to the jury.
During the course of the peijury trial, Ms. Butler attempted to explain that she had honestly believed she had no prior convictions when she testified to that fact at the previous trial. She contended that because an appeal had been taken she thought the conviction was not final, and she indicated that, having lost track of her attorney, she was unaware of the status of that appeal. This testimony was contradicted by that of Butler’s Delaware probation officer, who testified that at a June, 1985, probation revocation Ms. Butler stated that she had been aware since mid-1982 that her appeal had been denied. This testimony was corroborated by a tape recording of the 1985 hearing.
The Commonwealth presented the testimony of the court reporter from the 1984 trial, as well as the notes of testimony from that proceeding, to prove that Ms. Butler indeed had testified that she had never been convicted of a crime. Detective O’Leary, who investigated the 1984 prostitution charge and was a named defendant in Ms. Butler’s civil action, also testified that he had heard her deny any prior convictions.
Detective O’Leary testified that he had discovered the alleged perjury while reviewing Ms. Butler’s file approximately one year after her acquittal. He testified that he *11found the record of the 1982 conviction in a Department of Justice report in the file, and that he confirmed the information with the Delaware authorities. Although O’Leary could not explain why the Justice Department report, which is normally requested and filed at the time of arrest, was not discovered until a year after Ms. Butler’s acquittal, the detective characterized as merely coincidental the fact that the report was found after the civil suit was filed.
The defense then was denied the opportunity to cross-examine O’Leary for bias relating to his position as defendant in the civil suit. The trial court rejected Ms. Butler’s contention that O’Leary had a personal stake in the outcome of the perjury trial because Ms. Butler, if convicted, would be ineligible as a matter of law to testify in the civil suit.2 The trial court refused to allow any evidence of the civil suit, reasoning that defense counsel had ample opportunity to show bias, prejudice, or vindictiveness without injecting evidence of the lawsuit. No. 3671-85, slip op. at 12 (Court of Common Pleas, Delaware County, March 18, 1987). The trial court further opined that Ms. Butler was not prejudiced by this ruling because she was free to impeach him by other means. Cross-examination of Detective O’Leary was limited to his delay in investigating the alleged perjury and to the inconsistencies in his testimony.
Ms. Butler was convicted of perjury and sentenced to three to twenty-three months imprisonment. On appeal, the Superior Court reversed her conviction on two grounds. 367 Pa.Super. 453, 533 A.2d 105. First, the Superior Court concluded that the trial court erred in failing to hold an evidentiary hearing on Ms. Butler’s claim of prosecutorial vindictiveness. The court held that Ms. Butler should have been given an opportunity to present her claim of selective prosecution to the jury as a defense to the criminal charges. 367 Pa.Superior Ct. at 463, 533 A.2d at 110 (Superior Court, 1987). The court also concluded that the trial court erred in *12refusing to permit the cross-examination of Detective O’Leary as to the civil suit. The court reasoned that, in addition to her constitutional right to cross-examine a witness for possible motive to lie, Ms. Butler has a particular interest in testing the credibility of O’Leary, whose testimony was necessary under the “two witness” rule of perjury cases for corroboration of Butler’s statement at the 1984 trial. The Superior Court remanded the matter to the trial court, and the Commonwealth appealed.
The Commonwealth argues that the Superior Court erred in concluding that the question of selective prosecution should have been presented at trial. The Common7 wealth contends that a claim of prosecutorial vindictiveness is a question of law to be decided by the trial judge: The Commonwealth insists that although the record does not reflect whether a motion to dismiss was made on the basis of selective prosecution, the trial judge did consider and reject the claim. The Commonwealth also submits that, because the trial judge rejected the selective prosecution claim, the trial court properly rejected Mrs. Butler’s attempt to cross-examine Detective O’Leary for possible bias arising from the civil suit. Finally, the Commonwealth avers that the Superior Court incorrectly applied the “two-witness” rule of penury cases. We will address these claims seriatim.
Initially, it is necessary to note the distinction between the right of a party defendant to attempt to establish the bias of a witness who testified against her as it may reflect upon the credibility of the witness’ testimony, Commonwealth v. Cheatham, 429 Pa. 198, 239 A.2d 293 (1968), and a claim that government conduct is so offensive as to require the barring of the prosecution. The defense of prosecutorial vindictiveness is based upon the theory that due process prohibits a prosecutor from punishing a criminal defendant in retaliation for that defendant’s decision to exercise a constitutional right. Blackledge v. Perry, 417 U.S. 21, 94 S.Ct. 2098, 40 L.Ed.2d 628 (1974). Like other questions of outrageous government conduct, a claim of *13prosecutorial vindictiveness is a question of law, not fact. United States v. Krezdorn, 718 F.2d 1360 (5th Cir.1983), cert. denied, Krezdorn v. United States, 465 U.S. 1066, 104 S.Ct. 1416, 79 L.Ed.2d 742 (1984). The claim addresses itself to a constitutional defect in the institution of the prosecution. United States v. Berrigan, 482 F.2d 171 (3d Cir.1973). Such a claim is unrelated to the determination of guilt or innocence. United States v. Napper, 553 F.Supp. 231 (E.D.N.Y.1982). See also, Ford v. United States, 273 U.S. 593, 47 S.Ct. 531, 71 L.Ed. 793 (1927). A defendant who lodges a selective prosecution claim, therefore, does not have the right to present it to the jury. United States v. Berrigan, supra; United States v. Napper, supra.
In a federal criminal proceeding the claim of prosecutorial vindictiveness is instituted by means of a pre-trial motion to dismiss. Fed.R.Crim.P. 12(b)(2); see, e.g., United States v. Wallace, 578 F.2d 735 (8 Cir.1978), cert. denied, 439 U.S. 898, 99 S.Ct. 263, 58 L.Ed.2d 246 (1978); United States v. Taylor, 562 F.2d 1345 (1977), cert. denied, 432 U.S. 909, 97 S.Ct. 2958, 53 L.Ed.2d 1083 (1977). The case law of this Commonwealth is silent as to the means by which such a claim is to be raised; however, the motion to dismiss has been the accepted procedure for raising this claim. See, e.g., Commonwealth v. Lenig, 403 Pa.Super. 455, 589 A.2d 700 (1991).3 We now hold that a similar *14procedure is to be provided for lodging such a claim in the Pennsylvania courts. Although defense counsel in the instant case informed the court of the prosecutorial vindictiveness claim prior to the trial, the trial court summarily dismissed it as not being an issue in the case. This disposition did not give adequate consideration to appellant’s claim. Defense counsel should have been permitted to create a record to support this legal claim in the nature of a motion to dismiss.
We next address the Commonwealth’s contention that Ms. Butler was properly prohibited from cross-examining Detective O’Leary regarding the civil suit, based upon the trial court’s ruling that the civil suit was not at issue in the case but was a collateral matter which could confuse the jury. The Commonwealth maintains that the Superior Court erroneously characterized Detective O’Leary as a necessary witness under the “two-witness” rule, thereby ruling that the cross-examination should have been permitted.
It is well established that a criminal defendant has a right to cross-examine any adverse witness, whether or not that witness is “necessary” under the perjury rule, for the purpose of impeaching his credibility. The credibility of a witness may be impeached by evidence which tends to show that the witness had an interest in the outcome of the trial, Commonwealth v. Sullivan, 485 Pa. 392, 402 A.2d 1019 (1979), or that the witness’ testimony may be untruthful, Commonwealth v. Updegrove, 413 Pa. 599, 198 A.2d 534 (1964); or that the witness may possess a bias which colors his testimony, Commonwealth v. Collins, 519 Pa. 58, 545 A.2d 882 (1988); Commonwealth v. Hamm, 474 Pa. 487, 378 A.2d 1219 (1977). In the instant matter, Detective O’Leary was a defendant in a civil suit instituted by Ms. Butler, against whom he testified, and therefore, could be personally liable to Ms. Butler. This would provide a legitimate basis for a jury to infer bias on the part of Detective O’Leary, particularly where the outcome of the trial could materially affect the probability of success in the civil action. Certainly, a penury conviction would diminish Ms. *15Butler’s credibility in the eyes of a jury. Ms. Butler therefore should have been afforded the opportunity to cross-examine him with evidence of the civil suit. The trial court’s refusal to permit cross-examination in this area was also error.
Accordingly, the order of the Superior Court is affirmed, and the matter is remanded for proceedings consistent with this opinion.
FLAHERTY and McDERMOTT, JJ., file concurring and dissenting opinions. PAPADAKOS, J., files a dissenting opinion.. Ms. Butler claimed that she was forced to submit to a body cavity search, and was allegedly threatened that if she did not cooperate, she would be taken to a hospital and shackled for a gynecological examination.
. The statute precludes the testimony of one convicted of perjury for any purpose, "... unless the matter is one to redress or prevent injury or violence attempted, done or threatened to his person ..., in which case he shall be permitted to testify." 42 Pa.C.S. § 5922.
. As previously stated, a claim of prosecutorial vindictiveness, like claims of other types of prosecutorial misconduct, addresses itself to a concern that official misconduct should prevent the institution or prosecution of criminal charges against the defendant. See U.S. v. Krezdorn, 718 F.2d 1360 (5th Cir.1983), cert. denied, Krezdorn v. U.S., 465 U.S. 1066, 104 S.Ct. 1416, 79 L.Ed.2d 742 (1984). Other types of prosecutorial misconduct claims have traditionally been raised in this Commonwealth in the nature of a motion to dismiss. See, e.g., Commonwealth v. Bryant, 524 Pa. 564, 574 A.2d 590 (1990); In re Oxman, 496 Pa. 534, 437 A.2d 1169 (1981); Commonwealth v. Hoskins, 494 Pa. 600, 432 A.2d 149 (1981); Commonwealth v. Mitchell, 488 Pa. 75, 410 A.2d 1232 (1980).
Notwithstanding the traditional acceptance of this procedure, our criminal rules, unlike the federal rules herein discussed, make no express provision for such allegations to be raised. However, we recommend that the Criminal Procedural Rules Committee evaluate the need for establishing such a procedure.