opinion: Mr. Justice Whittaker
  delivered the opinion of the Court.
  Respondents, who are federal narcotics agents, arrested petitioner without a warrant in Cook County, Illinois, and, in the course of an incidental search, found narcotic drugs on his person which they seized. Respondents then delivered petitioner to the Cook County authorities who confined him in the county jail. In due course, the county grand jury returned an indictment charging petitioner with possessing the narcotics in violation of an Illinois statute. Soon after his arraignment and plea of “not guilty,” petitioner moved the court for an order suppressing the use of the narcotics as evidence in his impending criminal trial. After a full hearing, including the taking of evidence (not contained in this record), the court denied the motion.
  Before the case was reached for trial, petitioner brought the present action against respondents in the Federal District Court in Chicago to impound the narcotics (though he did not allege that respondents have possession of them) and to enjoin their use, and the respondents from testifying, at the trial of the criminal case in the state court. The very meager complaint alleged, in addition to the facts we have stated, only a few of the facts relating to petitioner’s arrest, and that he believes “respondents will be called to testify in [the state criminal] case that the petitioner unlawfully had in his possession the narcotic drugs seized by the respondents ....” It concluded with a prayer for the relief stated.
  Respondents moved to dismiss the complaint for failure to state a claim upon which relief could be granted. After a hearing, the District Court granted the motion and dismissed the action. On appeal, the Seventh Circuit affirmed. 275 F. 2d 932. To consider petitioner’s claim that the judgment is repugnant to controlling rules and decisions of this Court, we granted certiorari. 363 U. S. 840.
  We have concluded that the action was properly dismissed and that the judgment must be affirmed.
  Although the complaint alleged that the arrest was made without a warrant, there was no allegation that it was made without probable cause. In the absence of such an allegation the courts below could not, nor can we, assume that respondents arrested petitioner without probable cause to believe that he had committed or was committing a narcotics offense. And if they had such probable cause, the arrest, though without a warrant, was lawful and the subsequent search of petitioner’s person and the seizure of the found narcotics were validly made incidentally to a lawful arrest. Weeks v. United States, 232 U. S. 383, 392; Carroll v. United States, 267 U. S. 132, 158; Agnello v. United States, 269 U. S. 20, 30; Giordenello v. United States, 357 U. S. 480, 483; Draper v. United States, 358 U. S. 307, 310-311. For this reason alone the complaint failed to state a claim upon which relief could be granted.
  Nor did the complaint allege, even in conclusional terms, that petitioner does not have a plain and adequate remedy at law in the state court to redress any possible illegality in the arrest and incidental search and seizure. Indeed, the allegations of the complaint affirmatively show that petitioner does have such a remedy in the Illinois court and that he has actually prosecuted it there, but only to the point of an adverse interlocutory order. That court, whose jurisdiction first attached, retains jurisdiction over this matter to the exclusion of all other courts — certainly to the exclusion of the Federal District Court — until its duty has been fully performed, Harkrader v. Wadley, 172 U. S. 148, 164; Peck v. Jenness, 7 How. 612, 624-625, and it can determine this matter as well as, if not better than, the federal court. If, at the criminal trial, the Illinois court adheres to its interlocutory order on the suppression issue to petitioner's prejudice, he has an appeal to the Supreme Court of that State, and a right if need be to petition for “review by this Court of any federal questions involved.” Douglas v. City of Jeannette, 319 U. S. 157, 163. It is therefore clear that petitioner has a plain and adequate remedy at law in the criminal case pending against him in the Illinois court.
  There is still another cardinal reason why it was proper for the District Court to dismiss the complaint. We live in the jurisdiction of two sovereignties. Each has its own system of courts to interpret and enforce its laws, although in common territory. These courts could not perform their respective functions without embarrassing conflicts unless rules were adopted to avoid them. Such rules have been adopted. One of them is that an accused “should not be permitted to use the machinery of one sovereignty to obstruct his trial in the courts of the other, unless the necessary operation of such machinery prevents his having a fair trial.” Ponzi v. Fessenden, 258 U. S. 254, 260. Another is that federal courts should not exercise their discretionary power “to interfere with or embarrass threatened proceedings in state courts save in those exceptional cases which call for the interposition of a court of equity to prevent irreparable injury which is clear and imminent . . . .” Douglas v. City of Jeannette, supra, at 163.
  By this action, petitioner not only seeks to interfere with and embarrass the state court in his criminal case, but he also seeks completely to thwart its judgment by relitigating in a trial de novo in a federal court the very issue that he has already litigated in the state court. “If we were to sanction this intervention, we would expose every State criminal prosecution to insupportable disruption. Every question of procedural due process of law— with its far-flung and undefined range — would invite a flanking movement against the system of State courts by resort to the federal forum, with review if need be to this Court, to determine the issue. Asserted unconstitutionality in the impaneling and selection of the grand and petit juries, in the failure to appoint counsel, in the admission of a confession, in the creation of an unfair trial atmosphere, in the misconduct of the trial court [and, we may add, in the ruling of motions to suppress evidence, and in ruling the competency of witnesses and their testimony] — all would provide ready opportunities, which conscientious counsel might be bound to employ, to subvert the orderly, effective prosecution of local crime in local courts. To suggest these difficulties is to recognize their solution.” Stefanelli v. Minard, 342 U. S. 117, 123-124.
  Notwithstanding all of this, petitioner contends that the averments of his complaint were sufficient to entitle him to the relief prayed under the principles announced in Rea v. United States, 350 U. S. 214. But it is plain that the averments of this complaint do hot invoke or even approach the principles of the Rea case. That case did not hold, as petitioner’s contention assumes, that narcotic drugs lawfully seized by federal officers are inadmissible, or that such officers may not testify about their seizure, in state prosecutions. Such a concept would run counter to the express command of Congress that federal officers shall cooperate with the States in such investigations and prosecutions. See 21 U. S. C. § 198 (a). Indeed, the situation here is just the reverse of the situation in Rea. There, the accused had been indicted in a federal court for the unlawful acquisition of marihuana, and had moved in that court, under Rule 41 (e) of the Federal Rules of Criminal Procedure (18 U. S. C. App. Rule 41 (e)), for an order suppressing the use of the marihuana as evidence at the trial. After hearing, the District Court, finding that the accused’s arrest and search had been made by federal officers under an illegal warrant issued by a United States Commissioner, granted the motion to suppress. The effect of that order, under the express provisions of that Rule, was that the suppressed property “shall not be admissible in evidence at any hearing or trial.” Cf. Reina v. United States, 364 U. S. 507, 510-511. Despite that order, one of the arresting federal officers thereafter caused the accused to be rearrested and charged, in a state court, with possession of the same marihuana in violation of the State’s statute, and threatened to make the State’s case by his testimony and the use of the marihuana that the federal court had earlier suppressed under Rule 41 (e). Thereupon, to prevent the thwarting of the federal suppression order, petitioner moved the federal court to enjoin that conduct. That court denied the motion and its judgment was affirmed on appeal. On certiorari, this Court, acting under its supervisory power over the federal rules, which “extends to policing [their] requirements and making certain that they are observed,” 350 U. S., at 217, reversed the judgment, because “A federal agent [had] violated [and was about further to violate] the federal Rules governing searches and seizures — Rules prescribed by this Court and made effective after submission to the Congress. See 327 U. S. 821 et seq.” 350 U. S., at 217.
  How different are the facts in the present case! Here there is no allegation or showing that any proceedings ever were taken against petitioner under any federal rule or in any federal court. There has been no finding that petitioner’s arrest was unlawful or that the search of his person which yielded the narcotics was not incident to a lawful arrest and therefore proper. The state court’s finding — the only court involved and the only finding on the matter — is the other way. Nor is there even any allegation in the complaint that the arrest was not made upon probable cause, although it is admitted that the search was made incident to the arrest.
  It is clear that the complaint was properly dismissed.
  Affirmed.
  In this respect, the complaint alleged only that at the hearing on the motion to suppress "the following facts and circumstances were developed:
  “(a) The respondents testified that they had a certain building under surveillance where they had information that narcotic drugs were being sold. [Footnote 1 continued on p. 888.']
  “(b) That the respondents saw your petitioner approach the said building and enter the same; that a short time later they observed your petitioner leave the building whereupon they arrested him.
  “(c) That they could not state under oath whether he had the narcotic drugs in his possession before he entered the building under surveillance or not; that when they arrested him, they did not have a warrant for his arrest.”
  Article II, § 6, of the Illinois Constitution protects against unreasonable searches and seizures in substantially the same language as the Fourth Amendment. That State’s interpretation of its constitutional provision and its exclusionary rule, similar to the one followed in the federal courts, makes the Illinois law accord with the principles established by this Court for the federal system. See, e. g., People v. La Bostrie, 14 Ill. 2d 617, 620-623, 153 N. E. 2d 570, 572-574; People v. Tillman, 1 Ill. 2d 525, 529-530, 116 N. E. 2d 344, 346-347.
  “When a state court and a court of the United States may each take jurisdiction of a matter, the tribunal where jurisdiction first attaches holds it, to the exclusion of the other, until its duty is fully performed and the jurisdiction involved is exhausted; and this rule applies alike in both civil and criminal cases.” Harkrader v. Wadley, supra, at 164.
  “It is a doctrine of law too long established to require a citation of authorities, that . . . where the jurisdiction of a court, and the right of a plaintiff to prosecute his suit in it, have once attached, that right cannot be arrested or taken away by proceedings in another court. These rules have their foundation, not merely in comity, but on necessity. For if one may enjoin, the other may retort by injunction, and thus the parties be without remedy; being liable to a process for contempt in one, if they dare to proceed in the other.” Peck v. Jenness, supra, at 624-625.
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