concurring in part and dissenting in part.
I.
I agree with the Court that the purpose of the tolling provision in the statute of limitations before us, as evidenced by its language and its legislative history, is to avoid penalizing the Government when a criminal defendant cannot be indicted merely because no grand jury is sitting at the time the limitation period expires. In keeping with this purpose, the Government ought to be allowed to present a case prepared before the expiration of the limitation period to the grand jury when it next convenes, but it ought not to be allowed to take advantage of a nine-month extension to prepare a case which was not ready for submission before the end of the statutory period. I believe that the Court, therefore, is quite correct in rejecting the Government’s argument that the *227filing of any complaint which meets the formal requirements of Rule 3 of the Federal Rules of Criminal Procedure is sufficient to toll the statute of limitations. The Government’s argument would, in effect, allow it an additional nine months in every case. Rather, the view that I would accept as correct is that the only complaint that tolls the statute is one that begins effectively the criminal process prescribed by the Federal Rules.
I further agree with the Court that a complaint has effectively begun the criminal process only when all of the pre-indictment steps detailed in Rules 3, 4, and 5 have been taken. Only when it has been determined in the preliminary hearing required by Rule 5 that probable cause exists “to believe that an offense has been committed and that the defendant has committed it” can we say with any assurance that the complaint was not filed merely to extend the limitation period, but that it was a complaint which does what a complaint normally does, namely, starts the criminal procedure in motion. A speedy determination by a disinterested magistrate — the United States Commissioner — that probable cause exists also provides assurance that the Government in fact had a case ready for presentation to the grand jury before the limitation period expired. Thus I join the Court’s opinion insofar as it holds that only those complaints toll the statute of limitations which also start the criminal machinery in motion by leading to a preliminary hearing in compliance with Rules 3, 4, and 5.
II.
The facts of this case lead me to conclude, however, that the procedure outlined in Rule 5 was not followed, for a preliminary hearing was not scheduled within a reasonable time as the Rule requires. A person who is arrested must be taken before a Commissioner immediately and informed *228of his rights, and a preliminary examination to determine whether probable cause exists to believe that an offense has been committed and that he committed it must be held at that time or promptly thereafter. See Mallory v. United States, 354 U. S. 449, 454. This preliminary examination must be held promptly because it normally determines whether holding a defendant in custody pending action by the grand jury is warranted. Even when a defendant is not actually in custody but is free on bond a speedy hearing is still necessary, for he should not be required to maintain bond unless it has been determined by a disinterested Commissioner that probable cause exists. While normally when a summons is issued, rather than an arrest warrant, the period of time within which a preliminary examination must be held may be longer than when a defendant has been arrested, for he is not in custody nor need he post bond, in the special circumstances present here involving a statutory period of repose, it is important that the preliminary hearing be held with expedition similar to that necessary when the defendant is in custody or free on bond. A prompt preliminary hearing in this type of case serves as a check to prevent the Government from beginning a prosecution when a case is not ready for submission to the grand jury before the limitation period expires. I should think that, in view of this purpose, it would be sound practice, consistent with the statutory policy of repose, to hold the preliminary hearing and secure a magistrate’s determination of probable cause before the statutory period expires. Only then can it be certain that the Government has evidence showing probable cause at hand before the end of the limitation period. And, in an exceptional case, such as the one before us, where the complaint is filed so late that the hearing cannot be held within the limitation period, surely, in order to serve the statutory purpose, the hearing must be held with the same promptness as when *229a defendant is in custody or on bond, even though a summons, rather than an arrest warrant, was issued.
In this case the complaint was filed the day before the limitation period expired. In accordance with the Government’s wishes, the summons was made returnable 30 days later, and, at the Government’s subsequent request, the hearing date was postponed an additional week. In my view, to schedule a hearing to be held 36 days after the limitation period expires, when that hearing normally should have been held before the end of the statutory time for prosecution, is not to schedule it within the “reasonable time” which the Court itself says is required. Nor can it be said under the circumstances here present that the petitioner waived the right to have the probable cause determination made promptly. Whatever the burden on a defendant may be under other circumstances to move to accelerate a date fixed by a Commissioner upon an ex parte application of the Government, it would be unjust to apply any waiver concept here. Until the holding today there was no authoritative construction that the statute, read in conjunction with the Federal Criminal Rules, entitles the charged defendant to a hearing after issuance of a summons. There is no basis, therefore, for concluding that petitioner, by being silent under these circumstances, knowingly and consciously waived his right to a speedy hearing and determination of whether probable cause existed.
I would conclude that a preliminary hearing, which was to determine whether probable cause existed, was not held within a “reasonable time” as Rule 5 requires, and that since the Government did not fulfill all the requirements of this Rule, the complaint did not serve to institute the proper pre-indictment criminal procedure. It therefore, in my view, was not the type of complaint that tolls the statute of limitations under Internal Revenue Code § 6531, and petitioner’s prosecution should be barred.
*230III.
While it is not necessary, under my view of this case, to determine whether the complaint showed probable cause, since the Court reaches that issue, I believe it appropriate to express my disagreement with its conclusion. If the Court means that the standard of probable cause required for the issuance of a summons directing the defendant to appear for a preliminary hearing is the same as the standard required for issuance of a search warrant or an arrest warrant, which will place the defendant under immediate physical restraint, the complaint before us fails to demonstrate probable cause, for it clearly fails to meet the standards laid down in Giordenello v. United States, 357 U. S. 480, and Aguilar v. Texas, 378 U. S. 108.
This Court in Giordenello held that a finding of “probable cause” must be made by a “neutral and detached” magistrate who “assess [es] independently the probability that ... [an accused] committed the crime charged.” Giordenello v. United States, supra, at 486-487. (Emphasis added.) The Court also stated,
“The purpose of the complaint ... is to enable the appropriate magistrate ... to determine whether the ‘probable cause’ required to support a warrant exists. The Commissioner must judge for himself the persuasiveness of the facts relied on by a complaining officer to show probable cause. He should not accept without question the complainant’s mere conclusion that the person whose arrest is sought has committed a crime.” Id., at 486.
In order to make an independent determination that probable cause exists, the magistrate must be presented with more than the fact that the affiant or his sources are reliable and the affiant’s conclusion that the accused is believed to have committed a crime. As we stated in *231Aguilar v. Texas, supra, at 114, the magistrate or commissioner must also “be informed of some of the underlying circumstances” supporting the affiant’s belief that the accused has committed a crime. This statement was recently reaffirmed in United States v. Ventresca, 380 U. S. 102, 108. To allow a magistrate to find probable cause when a reliable affiant does no more than swear, as the agent did here, that his investigations led him to conclude that petitioner understated his income, is to remove the function of making an independent determination of probable cause from the hands of the magistrate and to place it in the hands of the agent.
The affidavit presented by the revenue agent in this case does no more than list the agent’s sources of information — examination of public and private records and interviews with third persons — and concludes that the petitioner understated his income. Without the slightest indication of what the agent’s examinations and interviews revealed, it is impossible for a “neutral and detached magistrate” to determine for himself whether probable cause existed. The agent need not set out all the information obtained, but, as we held in Aguilar, some of the underlying facts must be indicated.
I cannot accept the Court’s view that the nature of the offense charged in this case excuses the Government from setting out any of the facts underlying the conclusion that the petitioner understated his income. Surely, defendants in criminal tax cases — whether based upon a net worth theory or otherwise — are as entitled to a magistrate’s independent determination of “probable cause” as any other defendants. Furthermore, I do not believe it impossible, or even very difficult, for the Government to give some indication of the type of information obtained through its perusal of petitioner’s books and its interviews with third persons. But I do believe that it is impossible for a magistrate or commissioner to determine *232whether probable cause exists without some indication of the facts which led the affiant to his conclusion.
It is as true of the complaint before us as of the affidavit in Giordenello that “it is difficult to understand how the Commissioner could be expected to assess independently the probability that petitioner committed the crime charged.” 357 U. S., at 486-487. In my view, Giordenello and Aguilar require that the complaint not only state the ultimate conclusion that petitioner understated his income and set out the sources of information leading to that conclusion, but that it also set out some of the underlying facts upon which that conclusion is based. Since none of the underlying facts are set out in the complaint before us, I conclude that the probable cause standard of Giordenello and Aguilar is not met. For all the reasons stated, I would reverse the judgment of the Court of Appeals.