Probable Cause

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.


Probable Cause.—The concept of “probable cause” is central to the meaning of the warrant clause. Neither the Fourth Amendment nor the federal statutory provisions relevant to the area define “probable cause”; the definition is entirely a judicial construct. An applicant for a warrant must present to the magistrate facts sufficient to enable the officer himself to make a determination of probable cause. “In determining what is probable cause . . . [w]e are concerned only with the question whether the affiant had reasonable grounds at the time of his affidavit . . . for the belief that the law was being violated on the premises to be searched; and if the apparent facts set out in the affidavit are such that a reasonably discreet and prudent man would be led to believe that there was a commission of the offense charged, there is probable cause justifying the issuance of a warrant.”116 Probable cause is to be determined according to “the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.”117 Warrants are favored in the law and their use will not be thwarted by a hypertechnical reading of the supporting affidavit and supporting testimony.118 For the same reason, reviewing courts will accept evidence of a less “judicially competent or persuasive character than would have justified an officer in acting on his own without a warrant.”119 Courts will sustain the determination of probable cause so long as “there was substantial basis for [the magistrate] to conclude that” there was probable cause.120

Much litigation has concerned the sufficiency of the complaint to establish probable cause. Mere conclusory assertions are not enough.121 In United States v. Ventresca,122 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.123

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 States124 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,125 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. Texas126 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,127 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. Harris128 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.

subject and returned to the “totality of the circumstances” approach to evaluate probable cause based on an informant’s tip in Illinois v. Gates.129 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.”130 In evaluating probable cause, “[t]he 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.”131

116 Dumbra v. United States, 268 U.S. 435, 439, 441 (1925). “[T]he term ‘probable cause’ . . . means less than evidence which would justify condemnation.” Lock v. United States, 11 U.S. (7 Cr.) 339, 348 (1813). See Steele v. United States, 267 U.S. 498, 504–05 (1925). It may rest upon evidence that is not legally competent in a criminal trial, Draper v. United States, 358 U.S. 307, 311 (1959), and it need not be sufficient to prove guilt in a criminal trial. Brinegar v. United States, 338 U.S. 160, 173 (1949). See United States v. Ventresca, 380 U.S. 102, 107–08 (1965). An “anticipatory” warrant does not violate the Fourth Amendment as long as there is probable cause to believe that the condition precedent to execution of the search warrant will occur and that, once it has occurred, “there is a fair probability that contraband or evidence of a crime will be found in a specified place.” United States v. Grubbs, 547 U.S. 90, 95 (2006), quoting Illinois v. Gates, 462 U.S. 213, 238 (1983). “An anticipatory warrant is ‘a warrant based upon an affidavit showing probable cause that at some future time (but not presently) certain evidence of a crime will be located at a specified place.’” 547 U.S. at 94.

117 Brinegar v. United States, 338 U.S. 160, 175 (1949).

118 United States v. Ventresca, 380 U.S. 102, 108–09 (1965).

119 Jones v. United States, 362 U.S. 257, 270–71 (1960). Similarly, the preference for proceeding by warrant leads to a stricter rule for appellate review of trial court decisions on warrantless stops and searches than is employed to review probable cause to issue a warrant. Ornelas v. United States, 517 U.S. 690 (1996) (determinations of reasonable suspicion to stop and probable cause to search without a warrant should be subjected to de novo appellate review).

120 Aguilar v. Texas, 378 U.S. 108, 111 (1964). It must be emphasized that the issuing party “must judge for himself the persuasiveness of the facts relied on by a [complainant] to show probable cause.” Giordenello v. United States, 357 U.S. 480, 486 (1958). An insufficient affidavit cannot be rehabilitated by testimony after issuance concerning information possessed by the affiant but not disclosed to the magistrate. Whiteley v. Warden, 401 U.S. 560 (1971).

121 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).

122 380 U.S. 102 (1965).

123 380 U.S. at 109.

124 358 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 Whitely v. Warden, 401 U.S. 560, 566 (1971) (standards must be “at least as stringent” for warrantless arrest as for obtaining warrant).

125 362 U.S. 257 (1960).

126 378 U.S. 108 (1964).

127 393 U.S. 410 (1969). Both concurring and dissenting Justices recognized tension between Draper and Aguilar.See id. at 423 (Justice White concurring), id. at 429 (Justice Black dissenting and advocating the overruling of Aguilar).

128 403 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).

129 462 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.

130 462 U.S. at 213.

131 462 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. ___, No. 11–817, slip op. (2013).