Justice Brennan
delivered the opinion of the Court.
The impeachment exception to the exclusionary rule permits the prosecution in a criminal proceeding to introduce illegally obtained evidence to impeach the defendant’s own testimony. The Illinois Supreme Court extended this exception to permit the prosecution to impeach the testimony of all defense witnesses with illegally obtained evidence. 123 Ill. 2d 523, 528 N. E. 2d 723 (1988). Finding this extension inconsistent with the balance of values underlying our previous applications of the exclusionary rule, we reverse.
H-l
On the night of August 30, 1982, eight young boys returning home from a party were confronted by a trio of other boys who demanded money. When the eight boys refused to comply, one member of the trio produced a gun and fired into the larger group, killing one boy and seriously injuring another. When the police arrived, the remaining members of the larger group provided eyewitness accounts of the event and descriptions of the perpetrators.
The next evening, two detectives of the Chicago Police Department took 15-year-old Darryl James into custody as a suspect in the shooting. James was found at his mother’s beauty parlor sitting under a hair dryer; when he emerged, his hair was black and curly. After placing James in their car, the detectives questioned him about his prior hair color. He responded that the previous day his hair had been reddish brown, long, and combed straight back. The detectives questioned James again later at the police station, and he further stated that he had gone to the beauty parlor in order to have his hair “dyed black and curled in order to change his appearance.” App. 11.
The State subsequently indicted James for murder and attempted murder. Prior to trial, James moved to suppress the statements regarding his hair, contending that they were the fruit of a Fourth Amendment violation because the detectives lacked probable cause for his warrantless arrest. After an evidentiary hearing, the trial court sustained this motion and ruled that the statements would be inadmissible at trial.
At trial, five members of the larger group of boys testified for the State, and each made an in-court identification of the defendant. Each testified that the person responsible for the shooting had “reddish” hair, worn shoulder length in a slicked-back “butter” style. Each also recalled having seen James several weeks earlier at a parade, at which time James had the aforementioned hair color and style. At trial, however, his hair was black and worn in a “natural” style. Despite the discrepancy between the witnesses’ description and his present appearance, the witnesses stood firm in their conviction that James had been present and had fired the shots.
James did not testify in his own defense. He called as a witness Jewel Henderson, a friend of his family. Henderson testified that on the day of the shooting she had taken James to register for high school and that, at that time, his hair was black. The State then sought, over James’ objection, to introduce his illegally obtained statements as a means of impeaching the credibility of Henderson’s testimony. After determining that the suppressed statements had been made voluntarily, the trial court overruled James’ objection. One of the interrogating detectives then reported James’ prior admissions that he had reddish hair the night of the shooting and he dyed and curled his hair the next day in order to change his appearance. James ultimately was convicted of both murder and attempted murder and sentenced to 30 years’ imprisonment.
On appeal, the Illinois Appellate Court reversed James’ convictions and ordered a new trial. 153 Ill. App. 3d 131, 505 N. E. 2d 1118 (1987). The appellate court held that the exclusionary rule barred admission of James’ illegally obtained statements for the purpose of impeaching a defense witness’ testimony and that the resulting constitutional error was not harmless. However, the Illinois Supreme Court reversed. The court reasoned that, in order to deter the defendant from engaging in perjury “by proxy,” the impeachment exception to the exclusionary rule ought to be expanded to allow the State to introduce illegally obtained evidence to impeach the testimony of defense witnesses other than the defendant himself. The court therefore ordered James’ convictions reinstated. We granted certiorari. 489 U. S. 1010 (1989).
II
“There is no gainsaying that arriving at the truth is a fundamental goal of our legal system.” United States v. Havens, 446 U. S. 620, 626 (1980). But various constitutional rules limit the means by which government may conduct this search for truth in order to promote other values embraced by the Framers and cherished throughout our Nation’s history. “Ever since its inception, the rule excluding evidence seized in violation of the Fourth Amendment has been recognized as a principal mode of discouraging lawless police conduct. . . . [WJithout it the constitutional guarantee against unreasonable searches and seizures would be a mere ‘form of words.’” Terry v. Ohio, 392 U. S. 1, 12 (1968), quoting Mapp v. Ohio, 367 U. S. 643, 655 (1961). The occasional suppression of illegally obtained yet probative evidence has long been considered a necessary cost of preserving overriding constitutional values: “[T]here is nothing new in the realization that the Constitution sometimes insulates the criminality of a few in order to protect the privacy of us all.” Arizona v. Hicks, 480 U. S. 321, 329 (1987).
This Court has carved out exceptions to the exclusionary rule, however, where the introduction of reliable and probative evidence would significantly further the truth-seeking function of a criminal trial and the likelihood that admissibility of such evidence would encourage police misconduct is but a “speculative possibility.” Harris v. New York, 401 U. S. 222, 225 (1971). One exception to the rule permits prosecutors to introduce illegally obtained evidence for the limited purpose of impeaching the credibility of the defendant’s own testimony. This Court first recognized this exception in Walder v. United States, 347 U. S. 62 (1954), permitting the prosecutor to introduce into evidence heroin obtained through an illegal search to undermine the credibility of the defendant’s claim that he had never possessed narcotics. The Court explained that a defendant
“must be free to deny all the elements of the case against him without thereby giving leave to the Government to introduce by way of rebuttal evidence illegally secured by it, and therefore not available for its case in chief. Beyond that, however, there is hardly justification for letting the defendant affirmatively resort to perjurious testimony in reliance on the Government’s disability to challenge his credibility.” Id., at 65.
In Harris v. New York, supra, and Oregon v. Hass, 420 U. S. 714 (1975), the Court applied the exception to permit prosecutors to impeach defendants using incriminating yet voluntary and reliable statements elicited in violation of Miranda requirements. Finally, in United States v. Havens, supra, the Court expanded the exception to permit prosecutors to introduce illegally obtained evidence in order to impeach a defendant’s “answers to questions put to him on cross-examination that are plainly within the scope of the defendant’s direct examination.” Id., at 627.
This Court insisted throughout this line of cases that “evidence that has been illegally obtained ... is inadmissible on the government’s direct case, or otherwise, as substantive evidence of guilt.” Id., at 628. However, because the Court believed that permitting the use of such evidence to impeach defendants’ testimony would further the goal of truthseeking by preventing defendants from perverting the exclusionary rule “ ‘into a license to use perjury by way of a defense,”’ id., at 626 (citation omitted), and because the Court further believed that permitting such use would create only a “speculative possibility that impermissible police conduct will be encouraged thereby,” Harris, supra, at 225, the Court concluded that the balance of values underlying the exclusionary rule justified an exception covering impeachment of defendants’ testimony.
Ill
In this case, the Illinois Supreme Court held that our balancing approach in Walder and its progeny justifies expanding the scope of the impeachment exception to permit prosecutors to use illegally obtained evidence to impeach the credibility of defense witnesses. We disagree. Expanding the class of impeachable witnesses from the defendant alone to all defense witnesses would create different incentives affecting the behavior of both defendants and law enforcement officers. As a result, this expansion would not promote the truth-seeking function to the same extent as did creation of the original exception, and yet it would significantly undermine the deterrent effect of the general exclusionary rule. Hence, we believe that this proposed expansion would frustrate rather than further the purposes underlying the exclusionary rule.
The previously recognized exception penalizes defendants for committing perjury by allowing the prosecution to expose their perjury through impeachment using illegally obtained evidence. Thus defendants are discouraged in the first instance from “affirmatively resort[ing] to perjurious testimony.” Walder, supra, at 65. But the exception leaves defendants free to testify truthfully on their own behalf; they can offer probative and exculpatory evidence to the jury without opening the door to impeachment by carefully avoiding any statements that directly contradict the suppressed evidence. The exception thus generally discourages perjured testimony without discouraging truthful testimony.
In contrast, expanding the impeachment exception to encompass the testimony of all defense witnesses would not have the same beneficial effects. First, the mere threat of a subsequent criminal prosecution for perjury is far more likely to deter a witness from intentionally lying on a defendant’s behalf than to deter a defendant, already facing conviction for the underlying offense, from lying on his own behalf. Hence the Illinois Supreme Court’s underlying premise that a defendant frustrated by our previous impeachment exception can easily find a witness to engage in “perjury by proxy” is suspect.
More significantly, expanding the impeachment exception to encompass the testimony of all defense witnesses likely would chill some defendants from presenting their best defense — and sometimes any defense at all — through the testimony of others. Whenever police obtained evidence illegally, defendants would have to assess prior to trial the likelihood that the evidence would be admitted to impeach the otherwise favorable testimony of any witness they call. Defendants might reasonably fear that one or more of their witnesses, in a position to offer truthful and favorable testimony, would also make some statement in sufficient tension with the tainted evidence to allow the prosecutor to introduce that evidence for impeachment. First, defendants sometimes need to call “reluctant” or “hostile” witnesses to provide reliable and probative exculpatory testimony, and such witnesses likely will not share the defendants’ concern for avoiding statements that invite impeachment through contradictory evidence. Moreover, defendants often cannot trust even “friendly” witnesses to testify without subjecting themselves to impeachment, simply due to insufficient care or attentiveness. This concern is magnified in those occasional situations when defendants must call witnesses to testify despite having had only a limited opportunity to consult with or prepare them in advance. For these reasons, we have recognized in a variety of contexts that a party “cannot be absolutely certain that his witnesses will testify as expected.” Brooks v. Tennessee, 406 U. S. 605, 609 (1972). As a re-suit, an expanded impeachment exception likely would chill some defendants from calling witnesses who would otherwise offer probative evidence.
This realization alters the balance of values underlying the current impeachment exception governing defendants’ testimony. Our prior cases make clear that defendants ought not be able to “pervert” the exclusion of illegally obtained evidence into a shield for perjury, but it seems no more appropriate for the State to brandish such evidence as a sword with which to dissuade defendants from presenting a meaningful defense through other witnesses. Given the potential chill created by expanding the impeachment exception, the conceded gains to the truth-seeking process from discouraging or disclosing perjured testimony would be offset to some extent by the concomitant loss of probative witness testimony. Thus, the truth-seeking rationale supporting the impeachment of defendants in Walder and its progeny does not apply to other witnesses with equal force.
Moreover, the proposed expansion of the current impeachment exception would significantly weaken the exclusionary rule’s deterrent effect on police misconduct. This Court has characterized as a mere “speculative possibility,” Harris v. New York, 401 U. S., at 225, the likelihood that permitting prosecutors to impeach defendants with illegally obtained evidence would encourage police misconduct. Law enforcement officers will think it unlikely that the defendant will first decide to testify at trial and will also open the door inadvertently to admission of any illegally obtained evidence. Hence, the officers’ incentive to acquire evidence through illegal means is quite weak.
In contrast, expanding the impeachment exception to all defense witnesses would significantly enhance the expected value to the prosecution of illegally obtained evidence. First, this expansion would vastly increase the number of occasions on which such evidence could be used. Defense witnesses easily outnumber testifying defendants, both because many defendants do not testify themselves and because many if not most defendants call multiple witnesses on their behalf. Moreover, due to the chilling effect identified above, see supra, at 315-316, illegally obtained evidence holds even greater value to the prosecution for each individual witness than for each defendant. The prosecutor’s access to impeachment evidence would not just deter perjury; it would also deter defendants from calling witnesses in the first place, thereby keeping from the jury much probative exculpatory evidence. For both of these reasons, police officers and their superiors would recognize that obtaining evidence through illegal means stacks the deck heavily in the prosecution’s favor. It is thus far more than a “speculative possibility” that police misconduct will be encouraged by permitting such use of illegally obtained evidence.
The United States argues that this result is constitutionally acceptable because excluding illegally obtained evidence solely from the prosecution’s case in chief would still provide a quantum of deterrence sufficient to protect the privacy interests underlying the exclusionary rule. We disagree. Of course, a police officer might in certain situations believe that obtaining particular evidence through illegal means, re-suiting in,its suppression from the case in chief, would prevent the prosecution from establishing a prima facie case to take to a jury. In such situations, the officer likely would be deterred from obtaining the evidence illegally for fear of jeopardizing the entire case. But much if not most of the time, police officers confront opportunities to obtain evidence illegally after they have already legally obtained (or know that they have other means of legally obtaining) sufficient evidence to sustain a prima facie case. In these situations, a rule requiring exclusion of illegally obtained evidence from only the government’s case in chief would leave officers with little to lose and much to gain by overstepping constitutional limits on evidence gathering. Narrowing the exclusionary rule in this manner, therefore, would significantly undermine the rule’s ability “to compel respect for the constitutional guaranty in the only effectively available way — by removing the incentive to disregard it.” Elkins v. United States, 364 U. S. 206, 217 (1960). So long as we are committed to protecting the people from the disregard of their constitutional rights during the course of criminal investigations, inadmissibility of illegally obtained evidence must remain the rule, not the exception.
IV
The cost to the truth-seeking process of evidentiary exclusion invariably is perceived more tangibly in discrete prosecutions than is the protection of privacy values through deterrence of future police misconduct. When defining the precise scope of the exclusionary rule, however, we must focus on systemic effects of proposed exceptions to ensure that individual liberty from arbitrary or oppressive police conduct does not succumb to the inexorable pressure to introduce all incriminating evidence, no matter how obtained, in each and every criminal case. Our previous recognition of an impeachment exception limited to the testimony of defendants reflects a careful weighing of the competing values. Because expanding the exception to encompass the testimony of all defense witnesses would not further the truth-seeking value with equal force but would appreciably undermine the deterrent effect of the exclusionary rule, we adhere to the line drawn in our previous cases.
Accordingly, we hold that the Illinois Supreme Court erred in affirming James’ convictions despite the prosecutor’s use of illegally obtained statements to impeach a defense witness’ testimony. The court’s judgment is reversed, and the case is remanded for further proceedings not inconsistent with this opinion.
It is so ordered.
See generally Illinois v. Krull, 480 U. S. 340, 347 (1987) (when evaluating proposed exceptions to the exclusionary rule, this Court “has examined whether the rule’s deterrent effect will be achieved, and has weighed the likelihood of such deterrence against the costs of withholding reliable information from the truth-seeking process”); United States v. Leon, 468 U. S. 897, 908-913 (1984) (discussing balancing approach).
Certain Members of the Court have previously expressed their view that the exclusionary rule is designed not merely to deter police misconduct but also to prevent courts from becoming parties to the constitutional violation by admitting illegally obtained evidence at trial. See United States v. Leon, 468 U. S., at 931-938 (Brennan, J., joined by Marshall, J., dissenting); id., at 976-978 (Stevens, J., concurring in judgment in part and dissenting in part).
See Miranda v. Arizona, 384 U. S. 436 (1966).
See also Oregon v. Hass, 420 U. S. 714, 721 (1975) (“[TJrial court instructed the jury that the statements attributed to [defendant] could be used only in passing on his credibility and not as evidence of guilt”); Hands v. New York, 401 U. S. 222, 223 (1971) (same); Walder v. United States, 347 U. S. 62, 64 (1954) (same).
The dissent concedes, as it must, that “of course, false testimony can result from faulty recollection” as opposed to intentional lying. Post, at 326. Even assuming that Henderson’s testimony in this case (as opposed to the detective’s contrary testimony) was indeed false, nothing in the record suggests that Henderson intentionally committed perjury rather than honestly provided her best (even if erroneous) perception and recollection of events.
These reasons to doubt a party’s ability to control the testimony of his own witnesses led long ago to abandonment of the common-law rule that a party automatically “vouches for” and hence is inexorably bound by what the witnesses say. See, e. g., Fed. Rule Evid. 607 (“The credibility of a witness may be attacked by any party, including the party calling him”); see generally 3A J. Wigmore, Evidence § 899, p. 655 (J. Chadbourn rev. 1970) (“[E]very experienced lawyer knows that he is often required to call witnesses who happen to have some knowledge of the facts but whose trustworthiness he could not guarantee. There are also many occasions upon which a lawyer is surprised by the witness testifying in direct contradiction to a prior statement given to the attorney” (citation omitted)); cf. Chambers v. Mississippi, 410 U. S. 284 (1973) (state evidentiary rule precluding defendant from impeaching own witness after witness offered incriminating testimony violated due process). See also Imbler v. Pachtman, 424 U. S. 409, 426 (1976) (holding prosecutors absolutely immune from damages liability for having knowingly presented perjured witness testimony against criminal defendants, observing that the “veracity of witnesses in criminal cases frequently is subject to doubt before and after they testify .... If prosecutors were hampered in exercising their judgment as to the use of such witnesses by concern about resulting personal liability, [they often would refrain from calling such witnesses and hence] the triers of fact in criminal cases often would be denied relevant evidence”); id., at 446 (White, J., concurring in judgment) (“[0]ne of the effects of permitting suits for knowing use of perjured testimony will be detrimental to the [truth-seeking] process —prosecutors may withhold questionable but valuable testimony from the court”).
Apparently to minimize this concern, the Illinois Supreme Court suggested that prosecutors could impeach witnesses only with respect to statements that are “purposely presented by the defendant.” 123 Ill. 2d 523, 537, 528 N. E. 2d 723, 729 (1988). However, the court did not even purport to determine whether James had “purposely presented” Henderson’s testimony that his hair had been black on the day of the shooting, an omission that clearly highlights “the difficulty of determining whether particular testimony elicited from a defense witness was ‘purposely presented’ by the defendant.” Brief for United States as Amicus Curiae 21, n. 5. Given the inherent subjectivity of this proposed test, a defendant could hardly be confident that all witness statements that are actually inadvertent or surprising to the defendant will be found to be such by the trial court so as not to open the door to impeachment. This proposed limitation thus would not meaningfully blunt the chill imposed on defendants’ presentation of witnesses.
The Illinois Supreme Court also suggested that prosecutors could be allowed to impeach witnesses only with respect to statements offered on direct examination, perhaps recognizing that defendants likely would feel even more insecure about their witnesses’ ability to avoid statements triggering admissibility of suppressed evidence when responding to cross-examination by the prosecutor. We need not decide whether there is a salient distinction between direct and cross-examination in this context, cf. United States v. Havens, 446 U. S. 620 (1980) (rejecting such distinction with respect to defendants’ testimony), because even the more limited expansion of the impeachment exception would palpably inhibit defendants’ presentation of a defense.
Finally, the dissent embraces the Illinois Supreme Court’s suggestion that prosecutors could be allowed to impeach witnesses only when their testimony is in “direct conflict” with the illegally seized evidence. Post, at 325. The dissent suggests that judicial inquiry as to the inconsistency of various statements is “commonplace” under various rules of evidence. Post, at 325, n. 1. But the result of such an inquiry distinguishing between “direct” and “indirect” evidentiary conflicts is far from predictable. Indeed, the authority upon which the dissent relies to define a direct evi-dentiary conflict observes that “[s]uch is the possible variety of statement that it is often difficult to determine whether this inconsistency exists.” 3A Wigmore § 1040, at 1048. The ex ante uncertainty whether a court might find a witness’ testimony to pose a “direct” conflict and therefore trigger the impeachment exception likely will chill defendants’ presentation of potential witnesses in many cases.
Brief for United States as Amicus Curiae 18-22.
Indeed, the detectives who unlawfully detained James and elicited his incriminating statements already knew that there were several eyewitnesses to the shooting. Because the detectives likely believed that the exclusion of any statement they obtained from James probably would not have precluded the prosecution from making a prima facie case, an exclusionary rule applicable only to the prosecution’s case in chief likely would have provided little deterrent effect in this case.
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