In Knapp v. Schweitzer, 357 U. S. 371, the Court left open the question whether in the case of collaboration between state and federal officers a witness could successfully assert the federal privilege against self-incrimination in a state proceeding. In my view, that question should be answered here, for the records in these cases show such collaboration. Yet the majority of the Court ignores the question in affirming without opinion. Therefore, although I agree with and join the dissenting opinion of Mr. Justice Douglas, I add these additional views.
The petitioners in these cases were, held in contempt for failure to answer questions before a state grand jury investigating the bribery of police officials of New Orleans by persons conducting lottery operations within that city. From the nature of the questions asked petitioners, it’ is evident that they were suspected of engaging in lotteries and giving bribes. The District Attorney of the Parish of Orleans, under authority granted by state statute, offered petitioners full immunity from state prosecution for crimes, other than perjury, uncovered by the questioning. Nevertheless, petitioners refused to answer questions relating to bribery and their connections with lottery operations, pleading in justification of this refusal the federal privilege against self-incrimination. * «
The contempt proceedings and the state court reviews were had upon an agreed statement of facts. These stipulations recited that during the pendency of the state grand jury investigation “the Intelligence. Division, Internal Revenue Service of the United States, the United States Attorney for the Eastern District of Louisiana and the *232United States Grand Jury [had] been for several months and [were then] engaged in investigating some of the members of the New Orleans Police Department for income tax evasion, a felony under the laws of the United States.” In addition, the parties agreed that these investigations were wellpublicized and that, at the time of the instant proceedings, a number of federal. income tax indictments had been returned' against police officers; Further, it-was established that each of the petitioners had been requested to execute, and had executed, waivers of the statute of limitations on his federal tax liabilities for most of the years in question. Lastly, the parties stipulated:
“That there has existed, and now exists [at the time of the state proceeding], cooperation and collaboration between the District Attorney for.,the Parish of Orleans and the United States Attorney for the Eastern District of Louisiana and the.Internal Revenue Service of the United States of America and its investigators, as well as with the Police Bureau of Investigation of the City of New Orleans in reference to members of the New Orleans Police Department regarding public bribery and income tax evasion and that the Honorable Leon D. Hubert, Jr., District Attorney for the Parish of Orleans, has held conferences with the United States Attorney for the Eastern District of Louisiana regarding public bribery on the part of certain members of the New Orleans Police Department and income tax evasion, felonies under the law of the United States of America and the State of Louisiana.”
In Knapp v. Schweitzer, supra, which decided that the federal privilege against self-incrimination may not ordinarily be raised in a state proceeding, the Court said:
“Of course the Federal Government may not take advantage of this recognition of the States' autonomy *233in order to evade the Bill of Rights. If a federal officer should be a party to the compulsion of testimony by state agencies, the protection of the Fifth Amendment would come into play.. Such testimony is barred in a federal prosecution, see Byars v. United States, 273 U. S. 28. Whether, in a case of such collaboration between state and federal officers, the defendant could successfully assert his privilege in the state proceeding, we need not now decide, for the record before us is barren of evidence that the State was used as an instrument of federal prosecution or investigation. Petitioner’s assertion that a federal prosecuting attorney announced his intention of cooperating with staté officials in the prosecution of cases in a general field of criminal law presents a situation devoid of legal significance as a, joint state and federal endeavor.” 357 U. S., at 380.
I dissented from that decision on the ground that the state court had decided that the federal privilege did not obtain' on the seemingly false premise that information adduced in the state proceeding could not be used against the petitioner in a subsequent federal prosecution. But even accepting, for the purpose of argument, the validity of the Knapp result, I am of the view that the question which was not answered there should be‘considered here and resolved in favor of the petitioners.
The Knapp decision when taken in conjunction with Feldman v. United States, 322 U. S. 487, means that a person can be convicted of a federal crime on the basis of testimony which he is compelled to give in a state investigation. This opens vast opportunities for calculated efforts by state and federal officials working together to force a disclosure in a state proceeding and to convict on the basis of that disclosure in a federal proceeding. Such opportunities will not go unused unless the courts are vigilant to protect the rights of persons who find them*234selves faced with such coaction of federal and state prosecuting agencies. Such vigilance becomes increasingly required as the Federal Government, through prosecutions for tax evasion, moves into the criminal areas regúlated by the States.*
In the instant case the record shows clearly that state and federal authorities had launched a coordinated investigation into the suspected bribery by gamblers of New Orleans’ police officers. The State was interested primarily in the enforcement, of its public bribery statutes. The Federal Government sought to apprehend tax evaders.- • The state and federal agencies involved in this twofold investigation collaborated to obtain desired ends. Policemen suspected of taking bribes and gamblers suspected of giving them were called for questioning. Both were in jeopardy of prosecution: the police under state statute for taking bribes and under federal statute for income-tax evasion; the gamblers under state statute for giving bribes and under federal statutes for income tax evasion and for failure to pay the special stamp and excise taxes levied on gambling operations. Doubt which might have existed concerning federal interest in petitioners’ possible tax evasions was removed when petitioners were induced to waive the statute of limitations for relevant tax years.
The opinion in the Knapp case states that the protection of the Fifth Amendment comes into play if a federal' officer is a party to the compulsion of testimony by a state agency. 357 U. S. 371, 380. The threshold question then is whether the requisite relationship existed between the State District Attorney and the United States At*235torney and Internal Revenue agents. The stipulation, when read in the light of the known' facts, adequately shows that federal officers participated in the state action which sought to compel the- testimony of petitioners. That stipulation, signed by the state prosecutor, admits of “cooperation,” “collaboration,” and “conferences.” These terms viewed against the background of contemporaneous investigations by a federal grand jury, a state grand jury, the Police Bureau of Investigation of the City of New .Orleans, and the Intelligence Division of the Internal Revenue Service, all pointed at a group of persons which included petitioners, require the conclusion that the State was used as an instrument of federal investigation.
I come then to the question left open in the Knapp case: whether, where, as here, a State is used as an instrument of federal investigation, witnesses can successfully assert their federal privilege against self-incrimination in state proceedings. Knapp v. Schweitzer, supra, suggests that where testimony is compelled in such circumstances, the testimony would be inadmissible in a subsequent federal prosecution. See Byars v. United States, 273 U. S. 28. See also Feldman v. United States, 322 U. S. 487, 494. But this is only partial protection. To compel testimony in a federal investigation, a witness must be assured at the-outset complete immunity from any prosecution which might result from his compelled disclosures. Counselman v. Hitchcock, 142 U. S. 547; Brown v. Walker, 161 U. S. 591; Blau v. United States, 340 U. S. 159; Ullmann v. United States, 350 U. S. 422, 430. There is no indication that such protection obtains .here — that petitioners are protected from federal prosecutions which might result from their testimony even though that testimony is not admissible in the subsequent proceeding. Byars v. United States, supra, merely prohibits the introduction of illegally seized evidence and Knapp v. *236Schweitzer, supra, and Feldman v. United States, supra, speak merely of the non-use of the compelled testimony in a subsequent federal prosecution. None of these cases deals with the fruits of the compelled testimony, and defendants, like petitioners, who are forced to testify under circumstances similar to those here present, are left without the protection against self-incrimination intended by the Constitution. These cases, in my opinion, should be extended to prohibit any prosecution resulting from disclosures compelled under circumstances similar to those which exist here. But this is not an established principle and a witness is entitled to more than hopes of immunity when federal agencies seek to compel incriminatory testimony. Therefore, in my view, petitioners properly invoked their federal privilege against self-incrimination in the present proceeding and the con-tempts should be discharged. Cf. Rea v. United States, 350 U. S. 214; Bartkus v. Illinois, 359 U. S. 121, 164 (dissenting opinion).
Cf. Commissioner v. Wilcox, 327 U. S. 404; Rutkin v. United States, 343 U. S. 130; United States v. Catamaro, 354 U. S. 351; Rollinger v. United States, 208 F. 2d 109; Berra v. United States, 221 F. 2d 590; Schira v. Commissioner, 240 F. 2d 672; United States v. Wampler, 5 F. Supp. 796; United States v. Iozia, 104 F. Supp. 846.