378 U.S. 108 (1964)
Two Houston police officers applied to a local Justice of the Peace for a warrant to search petitioner's home for narcotics.1 In support of their application the officers submitted an affidavit reciting that the affiants had received reliable information from a credible person and did believe that heroin, marijuana, barbiturates and other narcotics and narcotic paraphernalia were being kept at the described premises for the purpose of sale and use contrary to law.2
The search warrant was issued on the strength of that affidavit alone.3 In executing the warrant the local police, together with federal officers, announced at petitioner's door that they were police with a warrant; upon hearing a commotion inside the house the officers forced their way in and seized petitioner in the act of attempting to dispose of a packet of narcotics.4
At his trial in state court petitioner objected through counsel to the introduction of evidence obtained through execution of the warrant, but the objections were overruled and the evidence was admitted.5 Petitioner was convicted of illegal possession of heroin and sentenced to twenty years in the state penitentiary.6
On appeal the Texas Court of Criminal Appeals affirmed the conviction, and the affirmance was upheld on rehearing.7 The Supreme Court granted a writ of certiorari to consider the constitutional questions presented, and the record shows that no other information was brought to the attention of the Justice of the Peace who issued the warrant.8
Whether the affidavit submitted in support of the application for a search warrant satisfied the constitutional requirements for obtaining a state search warrant under the Fourth and Fourteenth Amendments?9
Under the Fourth Amendment an officer may not properly issue a warrant to search a private dwelling unless probable cause can be found from facts or circumstances presented under oath or affirmation.10 Mere affirmance of belief or suspicion is not enough.11 An affidavit may be based on hearsay information and need not reflect the direct personal observations of the affiant. The magistrate must be informed of some of the underlying circumstances from which the informant concluded that the narcotics were where he claimed they were.12 The magistrate must also be informed of some of the underlying circumstances from which the officer concluded that the informant was credible or his information reliable.13
No. The affidavit provided no affirmative allegation that the affiant or the unidentified source spoke with personal knowledge. For all that appears, the source merely suspected, believed or concluded that there were narcotics in petitioner's possession.14 The magistrate therefore could not judge for himself the persuasiveness of the facts relied on to show probable cause and instead accepted without question the informant's suspicion or belief.15
The affidavit did not satisfy the constitutional requirements for obtaining a search warrant, and the evidence obtained as a result of the search warrant was inadmissible in petitioner's trial.16
Related opinions on this issue
Justice Harlan stated that but for Ker v. California, he would have voted to affirm the judgment of the Texas court.17 Given Ker, he could not escape the conclusion that to do so would tend to relax Fourth Amendment standards in derogation of law enforcement standards in the federal system.18 Contrary to what is suggested in the dissenting opinion of his Brother Clark in the present case, the standards laid down in Giordenello v. United States did in his view reflect constitutional requirements.19
Being unwilling to relax those standards for federal prosecutions, Justice Harlan concurred in the opinion of the Court.20
Justice Clark maintained that the affidavit was based not only on affirmance of belief but in addition upon reliable information from a credible person plus a week's surveillance by the affiants, rendering Nathanson inapposite.21 He noted that the affidavit alleged a source for the complainant's belief and therefore fell entirely outside the Giordenello holding, where no source of information had been stated.22 In his view the affidavit showed probable cause within the meaning of the Fourth Amendment.23
Justice Clark concluded that the Court had substituted a rigid academic formula for the unrigid standards of reasonableness and probable cause laid down by the Fourth Amendment itself.24