Supreme Court Interpretation of Probable Cause

The Fourth Amendment’s protection against unreasonable searches and seizures generally means law enforcement must have a warrant or “probable cause” to search someone’s property or make an arrest. But probable cause can come in many forms, and what qualifies as probable cause is something the Supreme Court has grappled with for many years.

What the Fourth Amendment Says

“The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”

Frequently Asked Questions

What It Means

Much litigation has concerned the sufficiency of the complaint to establish probable cause. Mere conclusory assertions are not enough.1 In United States v. Ventresca,2 however, an affidavit by a law enforcement officer asserting his belief that an illegal distillery was being operated in a certain place, explaining that the belief was based upon his own observations and upon those of fellow investigators, and detailing a substantial amount of these personal observations clearly supporting the stated belief, was held to be sufficient to constitute probable cause. Recital of some of the underlying circumstances in the affidavit is essential, the Court said, observing that where these circumstances are detailed, where reason for crediting the source of the information is given, and when a magistrate has found probable cause, the reliance on the warrant process should not be deterred by insistence on too stringent a showing.3

Probable Cause Based on Tips from Informants

Requirements for establishing probable cause through reliance on information received from an informant has divided the Court in several cases. Although involving a warrantless arrest, Draper v. United States4 may be said to have begun the line of cases. A previously reliable, named informant reported to an officer that the defendant would arrive with narcotics on a particular train, and described the clothes he would be wearing and the bag he would be carrying; the informant, however, gave no basis for his information. FBI agents met the train, observed that the defendant fully fit the description, and arrested him. The Court held that the corroboration of part of the informer’s tip established probable cause to support the arrest. A case involving a search warrant, Jones v. United States,5 apparently considered the affidavit as a whole to see whether the tip plus the corroborating information provided a substantial basis for finding probable cause, but the affidavit also set forth the reliability of the informer and sufficient detail to indicate that the tip was based on the informant’s personal observation. Aguilar v. Texas6 held insufficient an affidavit that merely asserted that the police had reliable information from a credible person that narcotics were in a certain place, and held that when the affiant relies on an informant’s tip he must present two types of evidence to the magistrate. First, the affidavit must indicate the informant’s basis of knowledge—the circumstances from which the informant concluded that evidence was present or that crimes had been committed—and, second, the affiant must present information that would permit the magistrate to decide whether or not the informant was trustworthy. Then, in Spinelli v. United States,7 the Court applied Aguilar in a situation in which the affidavit contained both an informant’s tip and police information of a corroborating nature.

The Court rejected the totality test derived from Jones and held that the informant’s tip and the corroborating evidence must be separately considered. The tip was rejected because the affidavit contained neither any information which showed the basis of the tip nor any information which showed the informant’s credibility. The corroborating evidence was rejected as insufficient because it did not establish any element of criminality but merely related to details which were innocent in themselves. No additional corroborating weight was due as a result of the bald police assertion that defendant was a known gambler, although the tip related to gambling. Returning to the totality test, however, the Court in United States v. Harris8 approved a warrant issued largely on an informer’s tip that over a two-year period he had purchased illegal whiskey from the defendant at the defendant’s residence, most recently within two weeks of the tip. The affidavit contained rather detailed information about the concealment of the whiskey, and asserted that the informer was a prudent person, that defendant had a reputation as a bootlegger, that other persons had supplied similar information about him, and that he had been found in control of illegal whiskey within the previous four years. The Court determined that the detailed nature of the tip, the personal observation thus revealed, and the fact that the informer had admitted to criminal behavior by his purchase of whiskey were sufficient to enable the magistrate to find him reliable, and that the supporting evidence, including defendant’s reputation, could supplement this determination.

The Court expressly abandoned the two-part Aguilar-Spinelli test and returned to the totality of the circumstances approach to evaluate probable cause based on an informant’s tip in Illinois v. Gates.9 The main defect of the two-part test, Justice Rehnquist concluded for the Court, was in treating an informant’s reliability and his basis for knowledge as independent requirements. Instead, a deficiency in one may be compensated for, in determining the overall reliability of a tip, by a strong showing as to the other, or by some other indicia of reliability.10 In evaluating probable cause, the task of the issuing magistrate is simply to make a practical, commonsense decision whether, given all the circumstances set forth in the affidavit before him, including the ‘veracity’ and ‘basis of knowledge’ of persons supplying hearsay information, there is a fair probability that contraband or evidence of a crime will be found in a particular place.11

Probable Cause vs. First Amendment Rights

Where the warrant process is used to authorize the seizure of books and other items that may be protected by the First Amendment, the Court has required the government to observe more exacting standards than in other cases.12 Seizure of materials arguably protected by the First Amendment is a form of prior restraint that requires strict observance of the Fourth Amendment. At a minimum, a warrant is required, and additional safeguards may be required for large-scale seizures. Thus, in Marcus v. Search Warrant,13 the seizure of 11,000 copies of 280 publications pursuant to warrant issued ex parte by a magistrate who had not examined any of the publications but who had relied on the conclusory affidavit of a policeman was voided. Failure to scrutinize the materials and to particularize the items to be seized was deemed inadequate, and it was further noted that police were provided with no guide to the exercise of informed discretion, because there was no step in the procedure before seizure designed to focus searchingly on the question of obscenity.14 A state procedure that was designed to comply with Marcus by the presentation of copies of books to be seized to the magistrate for his scrutiny prior to issuance of a warrant was nonetheless found inadequate by a plurality of the Court, which concluded that since the warrant here authorized the sheriff to seize all copies of the specified titles, and since [appellant] was not afforded a hearing on the question of the obscenity even of the seven novels [seven of 59 listed titles were reviewed by the magistrate] before the warrant issued, the procedure was constitutionally deficient.15

Confusion remains, however, about the necessity for and the character of prior adversary hearings on the issue of obscenity. In a later decision the Court held that, with adequate safeguards, no pre-seizure adversary hearing on the issue of obscenity is required if the film is seized not for the purpose of destruction as contraband (the purpose in Marcus and A Quantity of Books), but instead to preserve a copy for evidence.16 It is constitutionally permissible to seize a copy of a film pursuant to a warrant as long as there is a prompt post-seizure adversary hearing on the obscenity issue. Until there is a judicial determination of obscenity, the Court advised, the film may continue to be exhibited; if no other copy is available either a copy of it must be made from the seized film or the film itself must be returned.17

The seizure of a film without the authority of a constitutionally sufficient warrant is invalid; seizure cannot be justified as incidental to arrest, as the determination of obscenity may not be made by the officer himself.18 Nor may a warrant issue based solely on the conclusory assertions of the police officer without any inquiry by the magistrate into the factual basis for the officer’s conclusions.19 Instead, a warrant must be supported by affidavits setting forth specific facts in order that the issuing magistrate may ‘focus searchingly on the question of obscenity.’20 This does not mean, however, that a higher standard of probable cause is required in order to obtain a warrant to seize materials protected by the First Amendment. Our reference in Roaden to a ‘higher hurdle of reasonableness’ was not intended to establish a ‘higher’ standard of probable cause for the issuance of a warrant to seize books or films, but instead related to the more basic requirement, imposed by that decision, that the police not rely on the ‘exigency’ exception to the Fourth Amendment warrant requirement, but instead obtain a warrant from a magistrate.’21

In Stanford v. Texas,22 the Court voided a seizure of more than 2,000 books, pamphlets, and other documents pursuant to a warrant that merely authorized the seizure of books, pamphlets, and other written instruments concerning the Communist Party of Texas. The constitutional requirement that warrants must particularly describe the ‘things to be seized’ is to be accorded the most scrupulous exactitude when the ‘things’ are books, and the basis for their seizure is the ideas which they contain. . . . No less a standard could be faithful to First Amendment freedoms.23

However, the First Amendment does not bar the issuance or execution of a warrant to search a newsroom to obtain photographs of demonstrators who had injured several policemen, although the Court appeared to suggest that a magistrate asked to issue such a warrant should guard against interference with press freedoms through limits on the type, scope, and intrusiveness of the search.24

More on the Fourth Amendment

Unreasonable Seizures of Property

Students’ Rights Against Search and Seizure: New Jersey v. TLO

The Exclusionary Rule: Mapp v. Ohio


1.    Byars v. United States, 273 U.S. 28 (1927) (affiant stated he has good reason to believe and does believe that defendant has contraband materials in his possession); Giordenello v. United States, 357 U.S. 480 (1958) (complainant merely stated his conclusion that defendant had committed a crime). See also Nathanson v. United States, 290 U.S. 41 (1933).

2.    380 U.S. 102 (1965).

3.    380 U.S. at 109.

4.    8 U.S. 307 (1959). For another case applying essentially the same probable cause standard to warrantless arrests as govern arrests by warrant, see McCray v. Illinois, 386 U.S. 300 (1967) (informant’s statement to arresting officers met Aguilar probable cause standard). See also Whiteley v. Warden, 401 U.S. 560, 566 (1971) (standards must be at least as stringent for warrantless arrest as for obtaining warrant).

5.    362 U.S. 257 (1960).

6.    378 U.S. 108 (1964).

7.    393 U.S. 410 (1969). Both concurring and dissenting Justices recognized the tension between Draper and AguilarSee id. at 423 (Justice White concurring), id. at 429 (Justice Black dissenting and advocating the overruling of Aguilar).

8.    403 U.S. 573 (1971). See also Adams v. Williams, 407 U.S. 143, 147 (1972) (approving warrantless stop of motorist based on informant’s tip that may have been insufficient under Aguilar and Spinelli as basis for warrant).

9.    462 U.S. 213 (1983). Justice Rehnquist’s opinion of the Court was joined by Chief Justice Burger and by Justices Blackmun, Powell, and O’Connor. Justices Brennan, Marshall, and Stevens dissented.

10. 462 U.S. at 213.

11. 462 U.S. at 238. For an application of the Gates totality of the circumstances test to the warrantless search of a vehicle by a police officer, see, e.g. Florida v. Harris, 568 U.S. 237 (2013).

12.  Marcus v. Search Warrant, 367 U.S. 717, 730–31 (1961)Stanford v. Texas, 379 U.S. 476, 485 (1965). For First Amendment implications of seizures under the Federal Racketeer Influenced and Corrupt Organizations Act (RICO), see First Amendment: Obscenity and Prior Restraint.

13. 367 U.S. 717 (1961). See Kingsley Books v. Brown, 354 U.S. 436 (1957).

14. Marcus v. Search Warrant, 367 U.S. 717, 732 (1961).

15. A Quantity of Books v. Kansas, 378 U.S. 205, 210 (1964).

16. Heller v. New York, 413 U.S. 483 (1973).

17. Id. at 492–93. But cf. New York v. P.J. Video, Inc., 475 U.S. 868, 875 n.6 (1986), rejecting the defendant’s assertion, based on Heller, that only a single copy rather than all copies of allegedly obscene movies should have been seized pursuant to warrant.

18. Roaden v. Kentucky, 413 U.S. 496 (1973)See also Lo-Ji Sales v. New York, 442 U.S. 319 (1979)Walter v. United States, 447 U.S. 649 (1980). These special constraints are inapplicable when obscene materials are purchased, and there is consequently no Fourth Amendment search or seizure. Maryland v. Macon, 472 U.S. 463 (1985).

19. Lee Art Theatre, Inc. v. Virginia, 392 U.S. 636, 637 (1968) (per curiam).

20. New York v. P.J. Video, Inc., 475 U.S. 868, 873–74 (1986) (quoting Marcus v. Search Warrant, 367 U.S. 717, 732 (1961)).

21. New York v. P.J. Video, Inc., 475 U.S. 868, 875 n.6 (1986).

22. 379 U.S. 476 (1965).

23. 379 U.S. at 485–86. See also Marcus v. Search Warrant, 367 U.S. 717, 723 (1961).

24. Zurcher v. Stanford Daily, 436 U.S. 547 (1978)See id. at 566 (containing suggestion mentioned in text), and id. at 566 (Justice Powell concurring) (more expressly adopting that position). In the Privacy Protection Act, Pub. L. No. 96-440, 94 Stat. 1879 (1980), 42 U.S.C. § 2000aa, Congress provided extensive protection against searches and seizures not only of the news media and news people but also of others engaged in disseminating communications to the public, unless there is probable cause to believe the person protecting the materials has committed or is committing the crime to which the materials relate.

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