concurring.
I join the Court’s decision that a witness who has given immunized testimony may invoke the Fifth Amendment privilege at a later proceeding in response to questions based on his immunized testimony. Permitting a civil litigant to rely on prior immunized testimony to defeat an otherwise valid claim of privilege would be inconsistent with the purposes of the use-immunity statute, regardless of whether, had the witness answered voluntarily, his answers could have been used against him in a later criminal trial. The Court’s decision today does not reach the question whether such answers could later be admitted against the witness. In his dissenting opinion, Justice Stevens argues that Conboy may not assert the Fifth Amendment privilege precisely because his answers could not properly be used against him in a later criminal trial. Because I agree with Justice Stevens that such answers could not be properly used in a subsequent criminal trial, I write separately to explain why I believe respondent nevertheless retained his Fifth Amendment privilege.
If Conboy had voluntarily answered petitioners’ deposition questions, his answers would have been “directly or indirectly derived from” his prior testimony before the grand jury. The questions were based solely on the transcript of respondent’s grand jury testimony. There is no suggestion that the same or similar questions would have been asked had petitioners’ attorneys not obtained a transcript of the grand jury testimony. Thus, if respondent had answered the ques*265tions, his answers would not have been “derived from a legitimate source wholly independent of the compelled testimony.” Kastigar v. United States, 406 U. S. 441, 460 (1972).
The admission of such answers at a subsequent criminal prosecution would represent a substantial departure from the fundamental premise of this Court’s decision in Kastigar. In upholding the use-immunity statute against an attack based upon the Fifth Amendment privilege against self-incrimination, the Court concluded that use immunity affords a witness protection “as comprehensive as the protection afforded by the privilege.” Id., at 449. The Court stated that the statute “prohibits the prosecutorial authorities from using the compelled testimony in any respect,” id., at 453 (emphasis in original), and that it “provides a sweeping proscription of any use, direct or indirect, of the compelled testimony and any information derived therefrom,” id., at 460. If the prosecution could introduce answers elicited from a witness by questions that would not have been asked but for the witness’ immunized testimony, the protection afforded by use immunity would not be “as comprehensive as the protection afforded by the privilege.” Id., at 449.
I therefore agree with my Brother Stevens that answers to the questions posed by petitioners’ attorneys could not properly have been used at a subsequent criminal trial. It does not follow, however, that respondent can be compelled to answer. In this case it is conceded that, had respondent never given the immunized testimony before the grand jury, he would have been entitled to invoke the Fifth Amendment privilege in response to questions concerning the same subject matter as the questions asked at the deposition. The only question is whether respondent is barred from asserting the Fifth Amendment privilege because he previously testified under a statutory grant of immunity and because his answers to the deposition questions would be “directly or indirectly derived” from his prior immunized testimony.
*266In my view, a trial judge may not constitutionally compel a witness to give incriminating testimony solely upon a finding that the witness’ answers could not properly be used against him in a later criminal proceeding.1 This Court’s decision in *267Kastigar v. United States, supra, does not support such compulsion. In Kastigar the Court was concerned with a federal statute that permits a United States Attorney, a federal agency, or a duly authorized representative of Congress to grant use immunity and thereby compel a witness to give incriminating testimony. See 18 U. S. C. §§6002-6005. Kastigar itself involved a grant of use immunity conferred upon a witness called to testify before a grand jury. In upholding the use-immunity statute against constitutional attack, the Court held only that, pursuant to statutory authority to confer such immunity, the Government may constitutionally compel incriminating testimony in exchange for immunity from use or derivative use of that testimony. 406 U. S., at 462. Kastigar does not hold that a trial judge, acting without statutory authority to grant immunity, may rely on prior immunized testimony to overrule an otherwise valid assertion of the Fifth Amendment privilege by a deponent in a civil case.
Whatever justification there may be for requiring a witness to give incriminating testimony in aid of a criminal investigation after the Government has granted use immunity, there is no similar justification for compelling a witness to give incriminating testimony for the benefit of a private litigant when the Government has not chosen to grant immunity. Any interest served by compelling the testimony *268is insufficient to justify subjecting the witness to the risks that attend the compulsion of incriminating testimony.
Whenever a witness is forced to give incriminating testimony, there is a significant risk that fruits of that testimony will later be used against him. Further incriminating evidence that is derived from compelled testimony cannot always be traced back to its source:
“A witness who suspects that his compelled testimony was used to develop a lead will be hard pressed indeed to ferret out the evidence necessary to prove it. And of course it is no answer to say he need not prove it, for though the Court puts the burden of proof on the government, the government will have no difficulty in meeting its burden by mere assertion if the witness produces no contrary evidence. The good faith of the prosecuting authorities is thus the sole safeguard of the witness’ rights. [E]ven their good faith is not a sufficient safeguard. For the paths of information through the investigative bureaucracy may well be long and winding, and even a prosecutor acting in the best faith cannot be certain that somewhere in the depths of his investigative apparatus, often including hundreds of employees, there was not some prohibited use of the compelled testimony.” Kastigar v. United States, 406 U. S., at 469 (Marshall, J., dissenting).
See also Piccirillo v. New York, 400 U. S. 648, 567-568 (1971) (Brennan, J., dissenting from dismissal of certiorari); Speiser v. Randall, 357 U. S. 513, 525 (1958). If respondent is not allowed to assert the Fifth Amendment privilege, he may undergo numerous civil depositions, he may be forced to elaborate upon his original testimony,2 and his testimony *269may be broadly disseminated. As a result, he may face a much greater risk that tainted evidence will be used against him than he initially faced following the compulsion of the grand jury testimony. The opportunity to seek exclusion of tainted evidence is an incomplete protection, for “a court, at the time of the civil testimony, [cannot] predetermine the decision of the court in a subsequent criminal prosecution on the question whether the Government has met its burden of proving that ‘the evidence it proposes to use is derived from a legitimate source wholly independent of the compelled testimony.’” Ante, at 261 (quoting Kastigar v. United States, supra, at 460). Cf. Maness v. Meyers, 419 U. S. 449, 461-463 (1975).
It may be appropriate to subject a witness to these risks when the Government has conferred use immunity pursuant to statutory authorization, but the interests supporting compulsion of the testimony are far weaker here. In Kastigar the Court noted that the use-immunity statute advanced the Government interests in compelling incriminating testimony, 406 U. S., at 443-444, 446-447, and in leaving open the possibility of prosecuting the witness on the basis of “evidence from legitimate independent sources,” id., at 461. In this case, however, neither Congress nor the United States Attorney has made a similar expression of Government interest.3 The only public interest that would be served by forcing respondent to testify would be that of obtaining testi*270mony relevant to a private antitrust suit.4 Even that interest would not be substantially served.5
If he were compelled to answer petitioners’ deposition questions, Conboy would face a realistic risk that his testimony would lead to further incriminating evidence that he would be unable to exclude at a subsequent criminal prosecution. The interests underlying the use-immunity statute have no application here, and in my view the general interest in obtaining testimony cannot be considered an adequate substitute for those interests. I therefore join the Court in concluding that the Fifth Amendment does not permit a trial judge in a civil case to compel incriminating testimony solely upon a finding that the testimony would be “directly or *271indirectly derived from” the witness’ previously immunized testimony.
A witness is generally entitled to invoke the Fifth Amendment privilege against self-incrimination whenever there is a realistic possibility that his answer to a question can be used in any way to convict him of a crime. It need not be probable that a criminal prosecution will be brought or that the witness’ answer will be introduced in a later prosecution; the witness need only show a realistic possibility that his answer will be used against him. Moreover, the Fifth Amendment forbids not only the compulsion of testimony that would itself be admissible in a criminal prosecution, but also the compulsion of testimony, whether or not itself admissible, that may aid in the development of other incriminating evidence that can be used at trial. See Hoffman v. United States, 341 U. S. 479, 486 (1951).
The privilege is inapplicable only “if the testimony sought cannot possibly be used as a basis for, or in aid of, a criminal prosecution against the witness.” Brown v. Walker, 161 U. S. 591, 597 (1896). It has long been recognized that the court may require a witness to give testimony, including testimony that admits to involvement in a criminal act, when there is no possibility of future criminal charges being brought against the witness. For example, a witness may be compelled to testify concerning his involvement in a crime when he is protected from later prosecution by the Double Jeopardy Clause, see, e. g., Reina v. United States, 364 U. S. 507, 513 (1960) (dictum), by the applicable statute of limitations, see, e. g., United States v. Goodman, 289 F. 2d 256, 259 (CA4 1961), or by a pardon, see Brown v. Walker, supra, at 599-600. As Justice Brennan indicated in his dissenting opinion in Piccirillo v. New York, 400 U. S. 548, 564-565 (1971) (dissenting from dismissal of certiorari), this limitation upon the privilege against self-incrimination is derived from the language of the Fifth Amendment:
“Implicitly, of course, ‘in any criminal case’ suggests a limitation upon the reach of the privilege .... [I]f there is no possibility of a criminal case, then the privilege would not apply. And that is precisely the basis on which this Court has consistently upheld grants of immunity from Brown v. Walker, 161 U. S. 591 (1896), to Ullman v. United States, 350 U. S. 422 (1956).”
It has also been recognized that a court may compel a witness to testify when his answers could neither implicate him in any criminal conduct nor possibly lead to the discovery of past criminal conduct. See Hoffman v. *267United, States, supra; Heike v. United States, 227 U. S. 131, 142-145 (1913). This limitation, too, is implicit in the language of the constitutional guarantee, since a witness who has been forced to provide testimony that cannot incriminate him has not in any meaningful sense been “compelled in any criminal case to be a witness against himself.”
In this case, the Fifth Amendment privilege is fully applicable. Respondent remains subject to criminal prosecution, and his answers to the deposition questions asked by petitioners’ attorneys would both implicate him in criminal conduct and tend to lead to further incriminating information.
The questioning at the deposition went well beyond mere ratification of the accuracy of the grand jury transcript. Conboy was also called upon to answer again the identical questions asked before the grand jury. While it may be true that petitioners expected Conboy “only to ratify or *269confirm facts that were already known,” post, at 295 (Stevens, J., dissenting), there was no assurance in this case that Conboy’s answers, based upon his current recollection of events, would not provide details that were absent from his prior grand jury testimony.
As the Court observes, the Government interests that supported the compulsion of incriminating testimony in Kastigar would be undermined by the compulsion of respondent’s testimony in this case. The Government interest in preserving the chance to prosecute respondent in the future based on “legitimate independent” evidence would be compromised by the creation of additional immunized testimony. Ante, at 260-261.
Even if the United States Attorney consented to the trial judge’s compulsion of respondent’s answers, the judge’s action might be improper. As the Court notes, it is an open question whether the Government has statutory authority “to immunize the testimony of a witness in a civil proceeding when the Government determines that the public interest would be served.” Ante, at 261, n. 20 (emphasis added). Moreover, the constitutionality of such a statutory authorization remains open to doubt. Cf. Garrity v. New Jersey, 385 U. S. 493, 496 (1967) (declining to consider constitutionality of forfeiture-of-office statute which, in effect, allowed the authorities to compel a public officer, under threat of removal from office, to provide incriminating testimony in exchange for immunity from use or derivative use of that testimony at a criminal proceeding).
Indeed, this Court has not yet spoken as to the circumstances under which a trial court in a criminal case may compel a defense witness to testify concerning questions as to which he had previously testified before the grand jury or may compel the Government to secure such a witness’ testimony by granting him immunity. Cf. United States v. Praetorius, 622 F. 2d 1054, 1064 (CA2 1980); United States v. Morrison, 535 F. 2d 223, 229 (CA3 1976); United States v. Alessio, 528 F. 2d 1079 (CA9 1976); Earl v. United States, 124 U. S. App. D. C. 77, 80, n. 1, 361 F. 2d 531, 534, n. 1 (1966) (Burger, J.).
It is questionable whether the deposition testimony would be admissible at trial, in light of the limits that might have to be placed on cross-examination by the other civil litigants. Ante, at 259-260. Nor would respondent’s answers help petitioners obtain further relevant information, since petitioners already have access to respondent’s grand jury testimony.