Fourth Amendment: Search and Seizure

Chapter 17

Fourth Amendment: Search and Seizure

The Fourth Amendment, like many other provisions of the Bill of Rights, emerged in response to colonial experiences with the abusive police practices. Under English rule, the King’s agents were empowered to search dwellings and other places on the basis of mere suspicion or whim. Typically, these searches were conducted for the purposes of finding publications that criticized colonial rule. From this historical experience, the Fourth Amendment emerged as a guarantee against unreasonable searches and seizures. Consistent with the Bill of Rights generally, the Fourth Amendment initially was conceptualized as a safeguard against abuse by the federal government. Eventually, it was incorporated through the Fourteenth Amendment and thus made applicable to the states. The primary remedy for a Fourth Amendment violation is exclusion from trial of any evidence illegally obtained. The Supreme Court adopted the exclusionary rule as a federal remedy in Weeks v. United States (1914). Nearly half a century passed, however, before the Court in Mapp v. Ohio (1961) extended the exclusionary rule to state violations.

The Court has devoted much attention to defining and evolving key terms of the Fourth Amendment. In Delaware v. Prouse (1979), the Court found that police could not stop a motorist for a driver’s license and registration check minus some reasonable suspicion that the driver was engaged in criminal activity. The Court’s decision in United States v. Mendenhall (1980) gave meaning to the term “seizure,” which occurs only if a reasonable person would not feel free to leave an encounter with police. The ability of police to conduct a search or seizure, barring exceptional circumstances, is contingent upon a showing of probable cause. Probable cause is a general requirement for obtaining a search warrant. When informants are relied upon to establish probable cause, key factors may be the specificity of relevant facts and credibility of the source. In Illinois v. Gates (1983), it rejected the notion that probable cause could not be established on the basis of an anonymous tip. Although the informant’s veracity and reliability typically are relevant factors, the Court embraced an analysis that factored the totality of relevant circumstances. Second thoughts about the exclusionary rule led the Court, in United States v. Leon (1984), to adopt a “good faith” exception to its operation. Applied technology enables police to investigate and obtain information by methods that are less physically invasive. In Kyllo v. United States (2001), the Court determined that thermal imaging constituted a search for purposes of the Fourth Amendment. Although searches and seizures must be conditioned upon a showing of probable cause, pursuant to the Fourth Amendment’s explicit command, the Court has developed exceptions to this requirement. Its decision, in Board of Education of Independent School District No. 92 of Pottawatomie County v. Earls (2002), carved out an exception to the probable cause requirement for random drug testing of high school students engaged in extracurricular activities.

An exception to the general requirement that a warrant is needed before law enforcement conduct a search of seizure was established by the Court in what is referred to as the search incident to lawful arrest exception. In Chimel v. California (1969), the Court required that a search incident to arrest be limited to the area within the arrestee’s immediate control, and where it is justified by the interests in officer safety and in preventing evidence destruction. In United States v. Robinson (1973), the Court applied the Chimel analysis to a search of a cigarette pack found on the arrestee’s person. It held that the risks identified in Chimel are present in all custodial arrests, even when there is no specific concern about the loss of evidence or the threat to officers in a particular case. However, the court refused to extend the incident to a lawful arrest exception to searches of cell phone data. In Riley v. California (2014), the Court noted that that the warrantless search exception following an arrest exists for the purposes of protecting officer safety and preserving evidence, but that neither of these exceptions existed in the search of digital data on a cell phone. In addition, the Court observed that the amount of information that a modern cell phone is capable of carrying makes the privacy interests in their contents very high.

An essential threshold question considered by the Court is when there exists a “search” under the Fourth Amendment. In Katz v. United States (1967), the Court held that a Fourth Amendment “search” occurs when, and only when, a person has a “reasonable expectation of privacy” in the place searched. In Katz, the Court determined that a person has such a reasonable expectation of privacy in an enclosed phone booth. The Katz case also abandoned the earlier “trespass doctrine” which had held that a Fourth Amendment “search” occurs when a person’s property rights have been invaded by the government. However, the trespass doctrine gained new life in the more recent case of United States v. Jones (2012).

While the Katz case, and the test derived therefrom, had largely buried the old trespass doctrine, the Jones case breathed new life into the moribund doctrine. The trespass doctrine, as its name suggests, is tied to traditional property interests, and finds a Fourth Amendment search to have occurred when the government has invaded those interests in certain ways typically associated with common law trespass law. Now the Katz “reasonable expectation of privacy” test and the trespass doctrine exist side-by-side as alternatives ways that the Court can determine whether a Fourth Amendment “search” has occurred.

Another issue addressed by the Court is when consent to a search can waive the warrant requirement. The Court has ruled that as long as the consent is voluntary it constitutes a valid exception to the need for a warrant. One particularly thorny issue the Court has wrestled with involves the situation of when police can properly search premises without a warrant in the case of co-inhabitants who share common authority over the property. The general rule is that any co-inhabitant who shares common authority over the property may consent to a warrantless search. But what rule should apply when one co-habitant consents to a warrantless search, while another co-inhabitant objects to the same search? In Georgia v. Randolph (2006), the court ruled that if one of the co-inhabitants is present and objecting to the search the police are prohibited from continuing, even if another co-inhabitant consents to the search.

However, in Fernandez v. California (2014), the Court limited Randolph to situations where the objecting co-inhabitant is actually present and objecting to the police’s request for consent. In Fernandez, the defendant had objected, but after he was arrested and removed from the scene his co-inhabitant consented to the search that turned up incriminating evidence. The search was ruled constitutional.

Delaware v. Prouse

Citation: 440 U.S. 648.

Issue: Whether the police may “stop” to check and verify the driver’s license and registration.

Year of Decision: 1979.

Outcome: The police may not stop an automobile absent a “reasonable suspicion” that the passengers are involved in criminal activity.

Author of Opinion: Justice Byron White.

Vote: 8-1.

In the late 1960s, the Supreme Court began developing standards that expanded the authority of police to conduct searches and seizures. A momentum-building decision for this trend was Terry v. Ohio (1968). This case presented the question of whether, absent probable cause, “it is always unreasonable for a policeman to seize a person and subject him to a limited search for weapons.” Rather than adopt a fixed standard for all circumstances, the Terry Court determined that each case needed “to be decided on its own facts.” In Terry itself, the Court determined that it is reasonable under the Fourth Amendment for an officer “to conduct a carefully limited search of the outer clothing” for weapons when observation and experience leads him or her to conclude that the person may be armed and dangerous. This decision reflected a balancing of the “need” for police action, for purposes of protecting the officer’s and public’s safety, against the level of “intrusion” caused by the stop and frisk. Using this same test, the Court has articulated detailed rules regarding when the police can bring suspects in for questioning or subject them to fingerprinting or lineups.

Delaware v. Prouse presented the question of whether the police may “stop” automobiles simply to check their licenses and registrations. Prouse was pulled over in what the police officer referred to as a “routine” stop. The officer explained that “I saw the car in the area and wasn’t answering any complaints, so I decided to pull them off.” Unfortunately, for Prouse, the officer smelled marijuana smoke emanating from the vehicle and found marijuana lying in plain view on the floorboard of the vehicle. When Prouse was indicted for illegal possession of a controlled substance, he moved to suppress on the basis that the marijuana evidence would never have been discovered absent an unconstitutional stop.

In evaluating the constitutionality of the stop, the Court balanced the “need” for the stop against the governmental “intrusion”: “[T]he permissibility of a particular law enforcement practice is judged by balancing its intrusion on the individual’s Fourth Amendment interests against its promotion of legitimate governmental interests.”

In Prouse, the state argued that its interest in “promoting public safety upon its roads” outweighed the intrusion caused by the stop. The Court agreed that “the States have a vital interest in ensuring that only those qualified to do so are permitted to operate motor vehicles, that these vehicles are fit for safe operation, and hence that licensing, registration, and vehicle inspection requirements are being observed.” The court noted that drivers’ licenses “are issued periodically to evidence that the drivers holding them are sufficiently familiar with the rules of the road and are physically qualified to operate a motor vehicle.” In addition, the registration and vehicle inspection requirements “are designed to keep dangerous automobiles off the road.” The Court also found that automobile insurance requirements are important because they implement the “legitimate interest in seeing to it that its citizens have protection when involved in a motor vehicle accident.”

Even though the Court agreed that the state’s goals were legitimate, the Court doubted whether discretionary spot checks were “a sufficiently productive mechanism to justify the intrusion upon Fourth Amendment interests which such stops entail.” The Court concluded that the state had alternate mechanisms available for ensuring that drivers were carrying valid licenses without conducting random spot checks. The Court held that the police were free to pull motorists over when they observed violations of traffic laws and concluded that the police were free to check a motorist’s driver’s license and registration during such stops. Moreover, the Court assumed that unlicensed drivers were more likely to commit violations than licensed drivers. As a result, the Court concluded that “it must be assumed that finding an unlicensed driver among those who commit traffic violations is a much more likely event than finding an unlicensed driver by choosing randomly from the entire universe of drivers. [The] contribution to highway safety made by discretionary stops selected from among drivers generally will therefore be marginal at best.” In addition, the Court concluded that unlicensed drivers would be deterred by the possibility that they will be involved in accidents, or other violations, at which presentment of their license and registration will be required.

The Court also concluded that the state had alternate mechanisms for ensuring that cars were properly registered. The Court noted that all vehicles were required to have current license plates, and the Court noted that such plates could not be obtained absent compliance with the state’s registration requirements. As a result, the Court doubted that random stops would advance the state’s interest in keeping unregistered vehicles off the road.

In addition, the Court expressed concern about the police exercising unbridled discretion to stop motorists: “When there is not probable cause to believe that a driver is violating any one of the multitude of applicable traffic and equipment regulations—or other articulable basis amounting to reasonable suspicion that the driver is unlicensed or his vehicle unregistered—we cannot conceive of any legitimate basis upon which a patrolman could decide that stopping a particular driver for a spot check would be more productive than stopping any other driver. This kind of standardless and unconstrained discretion is the evil the Court has discerned when in previous cases it has insisted that the discretion of the official in the field be circumscribed, at least to some extent.”

By contrast, the Court found that the “intrusion” caused by a random vehicle stop was significant. The Court noted that an automobile is a basic and necessary method of transportation and noted that many people spend hours per day in their cars. “Were the individual subject to unfettered governmental intrusion every time he entered an automobile, the security guaranteed by the Fourth Amendment would be seriously circumscribed.”

The Court concluded by holding that, absent an “articulable and reasonable suspicion that a motorist is unlicensed or that an automobile is not registered, or that either the vehicle or an occupant is otherwise subject to seizure for violation of law,” the police may not stop the vehicle simply to check the driver’s license and registration.

Justice William Rehnquist authored a dissenting opinion. Because government has the right to require drivers’ licenses and vehicle registrations, he determined that it also may take the steps necessary to “enforce compliance.” Applying the need versus intrusion test, he argued that the “whole point of enforcing motor vehicle safety regulations is to remove from the road the unlicensed driver before he demonstrates why he is unlicensed. The Court would apparently prefer that the State check licenses and vehicle registrations as the wreckage is being towed away.”

The Court has departed from its “reasonable suspicion” requirement in the context of police roadblocks. In Michigan Department of State Police v. Sitz (1990), the Court upheld the constitutionality of sobriety checkpoints at which drivers were forced to stop and be checked for signs of intoxication. Drivers found to be intoxicated were arrested. In Sitz, the Court upheld the checkpoints, even though they were conducted without reasonable suspicion, because of the great need to apprehend drunk drivers in order to protect highway safety. However, in City of Indianapolis v. Edmond (2000), the Court struck down “drug interdiction checkpoints” at which drivers were stopped in an effort to uncover illegal drugs. The Court concluded that the checkpoints were seeking evidence of ordinary criminal wrongdoing, were unrelated to highway safety, and could not be justified absent evidence of reasonable suspicion that the drivers were involved in criminal activity.

Prouse is an important decision because it recognizes the right of automobile drivers and passengers to be free from governmental intrusions absent a reasonable suspicion that they are involved in criminal activities.


Justice WHITE delivered the opinion of the Court.

. . . The Fourth and Fourteenth Amendments are implicated in this case because stopping an automobile and detaining its occupants constitute a “seizure” within the meaning of those Amendments, even though the purpose of the stop is limited and the resulting detention quite brief. The essential purpose of the proscriptions in the Fourth Amendment is to impose a standard of “reasonableness” upon the exercise of discretion by government officials, including law enforcement agents, in order “ ‘to safeguard the privacy and security of individuals against arbitrary invasions . . . .’ ” Thus, the permissibility of a particular law enforcement practice is judged by balancing its intrusion on the individual’s Fourth Amendment interests against its promotion of legitimate governmental interests. Implemented in this manner, the reasonableness standard usually requires, at a minimum, that the facts upon which an intrusion is based be capable of measurement against “an objective standard,” whether this be probable cause or a less stringent test. In those situations in which the balance of interests precludes insistence upon “some quantum of individualized suspicion,” other safeguards are generally relied upon to assure that the individual’s reasonable expectation of privacy is not “subject to the discretion of the official in the field,” . . .

The marginal contribution to roadway safety possibly resulting from a system of spot checks cannot justify subjecting every occupant of every vehicle on the roads to a seizure—limited in magnitude compared to other intrusions but nonetheless constitutionally cognizable—at the unbridled discretion of law enforcement officials. To insist neither upon an appropriate factual basis for suspicion directed at a particular automobile nor upon some other substantial and objective standard or rule to govern the exercise of discretion “would invite intrusions upon constitutionally guaranteed rights based on nothing more substantial than inarticulate hunches . . . .” By hypothesis, stopping apparently safe drivers is necessary only because the danger presented by some drivers is not observable at the time of the stop. When there is not probable cause to believe that a driver is violating any one of the multitude of applicable traffic and equipment regulations—or other articulable basis amounting to reasonable suspicion that the driver is unlicensed or his vehicle unregistered—we cannot conceive of any legitimate basis upon which a patrolman could decide that stopping a particular driver for a spot check would be more productive than stopping any other driver. This kind of standardless and unconstrained discretion is the evil the Court has discerned when in previous cases it has insisted that the discretion of the official in the field be circumscribed, at least to some extent.

The “grave danger” of abuse of discretion, does not disappear simply because the automobile is subject to state regulation resulting in numerous instances of police-citizen contact. Only last Term we pointed out that “if the government intrudes . . . the privacy interest suffers whether the government’s motivation is to investigate violations of criminal laws or breaches of other statutory or regulatory standards.” There are certain “relatively unique circumstances,” in which consent to regulatory restrictions is presumptively concurrent with participation in the regulated enterprise. Otherwise, regulatory inspections unaccompanied by any quantum of individualized, articulable suspicion must be undertaken pursuant to previously specified “neutral criteria.”

An individual operating or traveling in an automobile does not lose all reasonable expectation of privacy simply because the automobile and its use are subject to government regulation. Automobile travel is a basic, pervasive, and often necessary mode of transportation to and from one’s home, workplace, and leisure activities. Many people spend more hours each day traveling in cars than walking on the streets. Undoubtedly, many find a greater sense of security and privacy in traveling in an automobile than they do in exposing themselves by pedestrian or other modes of travel. Were the individual subject to unfettered governmental intrusion every time he entered an automobile, the security guaranteed by the Fourth Amendment would be seriously circumscribed. As Terry v. Ohio, supra, recognized, people are not shorn of all Fourth Amendment protection when they step from their homes onto the public sidewalks. Nor are they shorn of those interests when they step from the sidewalks into their automobiles.

Accordingly, we hold that except in those situations in which there is at least articulable and reasonable suspicion that a motorist is unlicensed or that an automobile is not registered, or that either the vehicle or an occupant is otherwise subject to seizure for violation of law, stopping an automobile and detaining the driver in order to check his driver’s license and the registration of the automobile are unreasonable under the Fourth Amendment. This holding does not preclude the State of Delaware or other States from developing methods for spot checks that involve less intrusion or that do not involve the unconstrained exercise of discretion. Questioning of all oncoming traffic at roadblock-type stops is one possible alternative. We hold only that persons in automobiles on public roadways may not for that reason alone have their travel and privacy interfered with at the unbridled discretion of police officers. The judgment below is affirmed.


Bloom, Robert M., and Mark S. Brodin. Criminal Procedure: The Constitution and the Police. Frederick, MD: Wolters Kluwer, 2013, 67–98.

Thomas, George C., III. “Time Travel, Hovercrafts & the Framers: James Madison Sees the Future and Rewrites the Fourth Amendment.” Notre Dame Law Review 80 (2005): 451.

Weaver, Russell L. “Investigation & Discretion: The Terry Revolution at Forty (Almost).” Penn State Law Review 109 (2005): 1205.

United States v. Mendenhall

Citation: 446 U.S. 544.

Issue: Whether a woman was “seized” within the meaning of the Fourth Amendment when she was approached by Drug Enforcement Agents in an airport concourse.

Year of Decision: 1980.

Outcome: No seizure occurs unless a reasonable person in the suspect’s position would not feel free to leave.

Author of Opinion: Justice Potter Stewart.

Vote: 5-4.

Police-citizen encounters arise in a variety of contexts and may vary in their potential for intrusiveness. In some instances, the police have advance notice and can obtain a warrant to search or seize individuals. In other instances, the circumstances giving rise to the need to act can arise unexpectedly. For many years, the rules governing police-citizen encounters were vaguely defined and subject only to the Fourth Amendment’s general prohibition against “unreasonable” searches and seizures.

In general, the United States Supreme Court tended to impose a “warrant preference” for searches. However, the Court has articulated a number of exceptions to the warrant requirement. By contrast, warrants were not always required for “seizures.” For example, the Court has held that the police may arrest a citizen for a felony based only on a showing of “probable cause” to believe that the person to be arrested committed the crime. United States v. Watson (1976). In addition, in California v. Carney (1985) the Court allowed the police to stop and search vehicles based solely on probable cause.

The Court’s approach to street encounters changed significantly with its landmark decision in Terry v. Ohio (1968). In that case, the Court held that, when a police officer reasonably concludes, in light of his experience, that criminal activity is afoot and that the suspect is both armed and dangerous, the office may be entitled to conduct a “stop and frisk.” Terry represented a major break from prior precedent because it seemed to sustain seizures (the stop) and searches (the frisk) based on something less than probable cause. In reaching its decision, the Court balanced the need for the search against the level of intrusion imposed on the suspect’s privacy. Because the officer perceived that a robbery was about to take place, the need for action was great. Likewise, given that the officer did nothing more than “stop” and “frisk” the suspects, the intrusion was deemed to be relatively minor compared to the need.

In post-Terry cases, the Court has applied the “need-intrusion” test in a number of other contexts to give police greater authority to search and seize. In Mendenhall, the Court was asked to apply the Terry balancing test to airport investigative stops. Mendenhall arrived at the Detroit Metropolitan Airport early one morning and was approached by Drug Enforcement Agency agents who suspected that she was transporting illegal narcotics. The agents asked Mendenhall for her driver’s license and identification. Mendenhall’s plane ticket was issued in the name of “Annette Ford,” and Mendenhall explained that she “just felt like using that name.”

After the agent learned that Mendenhall had been in California for only two days, the interviewing officer identified himself as a DEA agent. At that point, Mendenhall became “quite shaken, extremely nervous” and “had a hard time speaking.” After returning the airline ticket and driver’s license to Mendenhall, the DEA agent asked the respondent if she would accompany him to the airport DEA office for further questions. She did not respond to the request, but followed him to the DEA office. At the office the agent asked the respondent if she would allow a search of her person and handbag and told her that she had the right to decline the search if she desired. She responded: “Go ahead.” In the ensuing search, the officers found that Mendenhall was carrying heroin. She was charged and convicted.

The Court first considered whether, when the DEA agent approached Mendenhall, he “seized” her within the meaning of the Fourth Amendment. In resolving that question, the Court began by defining the term “seizure.” The Court concluded that “not all personal intercourse between policemen and citizens involves ‘seizures’ of persons.” Indeed, the police are free to speak with citizens on the street and ask them questions, and a seizure occurs only “when the officer, by means of physical force or show of authority, has in some way restrained the liberty of a citizen.” In the Court’s view, a seizure can exist within the meaning of the Fourth Amendment only if, in view of all of the circumstances surrounding the incident, “a reasonable person would have believed that he was not free to leave.” Factors that might enter into a court’s analysis regarding the seizure issue are the following: whether the individual is surrounded by threatening police officers; whether the officer displayed a weapon; whether there was some physical touching of the person of the citizen; or whether the use of language or tone of voice indicated that compliance with the officer’s request might be compelled.

On the Mendenhall facts, the Court held that no “seizure” had occurred. The Court emphasized that Mendenhall was approached in a public concourse by officers who were not wearing uniforms and displayed no weapons. In addition, the officers did not demand, but instead requested, the right to examine Mendenhall’s identification and ticket. Such conduct, without more, did not amount to an intrusion upon any constitutionally protected interest. As a result, the Court concluded that “nothing in the record suggests that the respondent had any objective reason to believe that she was not free to end the conversation in the concourse and proceed on her way, and for that reason we conclude that the agents’ initial approach to her was not a seizure.”

In dicta, the Court recognized that a short investigative stop might be justified based on something less than probable cause. Based on the Terry “need-intrusion” test, the Court indicated that such a seizure might be justified based only on a showing of “reasonable suspicion” that the suspect was involved in criminal activity. In later cases, the Court has fleshed out the requirements for other types of investigative encounters. For example, in Dunaway v. New York (1979), the Court held that probable cause was required in order for the police to take a suspect to the station house for custodial interrogation. Likewise, in Davis v. Mississippi (1969), the Court held that probable cause was required to take a suspect to the station house for fingerprinting. However, in Hayes v. Florida (1985), the Court indicated that it might uphold a brief detention for fingerprinting based only on a reasonable suspicion that the suspect is involved in criminal activity.

Justice Byron White, joined by three other justices, dissented, arguing that Mendenhall was “seized” within the meaning of the Fourth Amendment when she was escorted from the public area of the terminal to the DEA office for questioning and a strip search of her person. He doubted that she was free to leave, especially once she arrived at the DEA office. “[Because] Ms. Mendenhall was being illegally detained at the time of the search of her person, her suppression motion should have been granted in the absence of evidence to dissipate the taint.”

Mendenhall is important because it helps define the rules applicable to investigative stops. In general, a “seizure” occurs only when a reasonable person in the suspect’s position would not feel free to leave. In order to justify the most minimal seizure, an investigative stop, nothing more need be shown than a “reasonable suspicion” that the suspect is involved in criminal activity.


Mr. Justice STEWART announced the judgment of the Court and delivered an opinion, in which Mr. Justice REHNQUIST joined.

. . . The Fourth Amendment provides that “the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated . . . .” There is no question in this case that the respondent possessed this constitutional right of personal security as she walked through the Detroit Airport, for “the Fourth Amendment protects people, not places.” Here the Government concedes that its agents had neither a warrant nor probable cause to believe that the respondent was carrying narcotics when the agents conducted a search of the respondent’s person. It is the Government’s position, however, that the search was conducted pursuant to the respondent’s consent, and thus was excepted from the requirements of both a warrant and probable cause. . . .

The Fourth Amendment’s requirement that searches and seizures be founded upon an objective justification, governs all seizures of the person, “including seizures that involve only a brief detention short of traditional arrest.” Accordingly, if the respondent was “seized” when the DEA agents approached her on the concourse and asked questions of her, the agents’ conduct in doing so was constitutional only if they reasonably suspected the respondent of wrongdoing. But “[o]bviously, not all personal intercourse between policemen and citizens involves ‘seizures’ of persons. Only when the officer, by means of physical force or show of authority, has in some way restrained the liberty of a citizen may we conclude that a ‘seizure’ has occurred. . . .”

We adhere to the view that a person is “seized” only when, by means of physical force or a show of authority, his freedom of movement is restrained. Only when such restraint is imposed is there any foundation whatever for invoking constitutional safeguards. The purpose of the Fourth Amendment is not to eliminate all contact between the police and the citizenry, but “to prevent arbitrary and oppressive interference by enforcement officials with the privacy and personal security of individuals.” As long as the person to whom questions are put remains free to disregard the questions and walk away, there has been no intrusion upon that person’s liberty or privacy as would under the Constitution require some particularized and objective justification. . . .

We conclude that a person has been “seized” within the meaning of the Fourth Amendment only if, in view of all of the circumstances surrounding the incident, a reasonable person would have believed that he was not free to leave. Examples of circumstances that might indicate a seizure, even where the person did not attempt to leave, would be the threatening presence of several officers, the display of a weapon by an officer, some physical touching of the person of the citizen, or the use of language or tone of voice indicating that compliance with the officer’s request might be compelled. In the absence of some such evidence, otherwise inoffensive contact between a member of the public and the police cannot, as a matter of law, amount to a seizure of that person.

On the facts of this case, no “seizure” of the respondent occurred. The events took place in the public concourse. The agents wore no uniforms and displayed no weapons. They did not summon the respondent to their presence, but instead approached her and identified themselves as federal agents. They requested, but did not demand to see the respondent’s identification and ticket. Such conduct without more, did not amount to an intrusion upon any constitutionally protected interest. The respondent was not seized simply by reason of the fact that the agents approached her, asked her if she would show them her ticket and identification, and posed to her a few questions. Nor was it enough to establish a seizure that the person asking the questions was a law enforcement official. In short, nothing in the record suggests that the respondent had any objective reason to believe that she was not free to end the conversation in the concourse and proceed on her way, and for that reason we conclude that the agents’ initial approach to her was not a seizure.

Our conclusion that no seizure occurred is not affected by the fact that the respondent was not expressly told by the agents that she was free to decline to cooperate with their inquiry, for the voluntariness of her responses does not depend upon her having been so informed. We also reject the argument that the only inference to be drawn from the fact that the respondent acted in a manner so contrary to her self-interest is that she was compelled to answer the agents’ questions. It may happen that a person makes statements to law enforcement officials that he later regrets, but the issue in such cases is not whether the statement was self-protective, but rather whether it was made voluntarily. . . .

Although we have concluded that the initial encounter between the DEA agents and the respondent on the concourse at the Detroit Airport did not constitute an unlawful seizure, it is still arguable that the respondent’s Fourth Amendment protections were violated when she went from the concourse to the DEA office. Such a violation might in turn infect the subsequent search of the respondent’s person. . . .

The question whether the respondent’s consent to accompany the agents was in fact voluntary or was the product of duress or coercion, express or implied, is to be determined by the totality of all the circumstances, and is a matter which the Government has the burden of proving. The respondent herself did not testify at the hearing. The Government’s evidence showed that the respondent was not told that she had to go to the office, but was simply asked if she would accompany the officers. There were neither threats nor any show of force. The respondent had been questioned only briefly, and her ticket and identification were returned to her before she was asked to accompany the officers. . . .

Because the search of the respondent’s person was not preceded by an impermissible seizure of her person, it cannot be contended that her apparent consent to the subsequent search was infected by an unlawful detention. There remains to be considered whether the respondent’s consent to the search was for any other reason invalid. The District Court explicitly credited the officers’ testimony and found that the “consent was freely and voluntarily given.” There was more than enough evidence in this case to sustain that view. First, we note that the respondent, who was 22 years old and had an 11th-grade education, was plainly capable of a knowing consent. Second, it is especially significant that the respondent was twice expressly told that she was free to decline to consent to the search, and only thereafter explicitly consented to it. Although the Constitution does not require “proof of knowledge of a right to refuse as the sine qua non of an effective consent to a search,” such knowledge was highly relevant to the determination that there had been consent. And, perhaps more important for present purposes, the fact that the officers themselves informed the respondent that she was free to withhold her consent substantially lessened the probability that their conduct could reasonably have appeared to her to be coercive.

Counsel for the respondent has argued that she did in fact resist the search, relying principally on the testimony that when she was told that the search would require the removal of her clothing, she stated to the female police officer that “she had a plane to catch.” But the trial court was entitled to view the statement as simply an expression of concern that the search be conducted quickly. The respondent had twice unequivocally indicated her consent to the search, and when assured by the police officer that there would be no problem if nothing were turned up by the search, she began to undress without further comment.

Counsel for the respondent has also argued that because she was within the DEA office when she consented to the search, her consent may have resulted from the inherently coercive nature of those surroundings. But in view of the District Court’s finding that the respondent’s presence in the office was voluntary, the fact that she was there is little or no evidence that she was in any way coerced. And in response to the argument that the respondent would not voluntarily have consented to a search that was likely to disclose the narcotics that she carried, we repeat that the question is not whether the respondent acted in her ultimate self-interest, but whether she acted voluntarily.

We conclude that the District Court’s determination that the respondent consented to the search of her person “freely and voluntarily” was sustained by the evidence and that the Court of Appeals was, therefore, in error in setting it aside. Accordingly, the judgment of the Court of Appeals is reversed, and the case is remanded to that court for further proceedings.

Mr. Justice WHITE, with whom Mr. Justice BRENNAN, Mr. Justice MARSHALL, and Mr. Justice STEVENS join, dissenting.

The Court today concludes that agents of the Drug Enforcement Administration (DEA) acted lawfully in stopping a traveler changing planes in an airport terminal and escorting her to a DEA office for a strip-search of her person. This result is particularly curious because a majority of the Members of the Court refuse to reject the conclusion that Ms. Mendenhall was “seized,” while a separate majority decline to hold that there were reasonable grounds to justify a seizure. Mr. Justice STEWART concludes that the DEA agents acted lawfully, regardless of whether there were any reasonable grounds for suspecting Ms. Mendenhall of criminal activity, because he finds that Ms. Mendenhall was not “seized” by the DEA agents, even though throughout the proceedings below the Government never questioned the fact that a seizure had occurred necessitating a showing of antecedent reasonable suspicion. Mr. Justice POWELL’s opinion concludes that even though Ms. Mendenhall may have been “seized,” the seizure was lawful because her behavior while changing planes in the airport provided reasonable suspicion that she was engaging in criminal activity. The Court then concludes, based on the absence of evidence that Ms. Mendenhall resisted her detention, that she voluntarily consented to being taken to the DEA office, even though she in fact had no choice in the matter. This conclusion is inconsistent with our recognition that consent cannot be presumed from a showing of acquiescence to authority, and it cannot be reconciled with our decision last Term in Dunaway v. New York.

Beginning with Terry v. Ohio, the Court has recognized repeatedly that the Fourth Amendment’s proscription of unreasonable “seizures” protects individuals during encounters with police that do not give rise to an arrest. In Terry we “emphatically reject[ed]” the notion that a “stop” “is outside the purview of the Fourth Amendment because . . . [it is not a] ‘seizure’ within the meaning of the Constitution.” We concluded that “the sounder course is to recognize that the Fourth Amendment governs all intrusions by agents of the public upon personal security, and to make the scope of the particular intrusion, in light of all the exigencies of the case, a central element in the analysis of reasonableness.” Applying this principle, “[w]e have recognized that in some circumstances an officer may detain a suspect briefly for questioning although he does not have ‘probable cause’ to believe that the suspect is involved in criminal activity, as is required for a traditional arrest. However, we have required the officers to have a reasonable suspicion, based on objective facts, that the individual is involved in criminal activity.”

Throughout the lower court proceedings in this case, the Government never questioned that the initial stop of Ms. Mendenhall was a “seizure” that required reasonable suspicion. Rather, the Government sought to justify the stop by arguing that Ms. Mendenhall’s behavior had given rise to reasonable suspicion because it was consistent with portions of the so-called “drug courier profile,” an informal amalgam of characteristics thought to be associated with persons carrying illegal drugs. Having failed to convince the Court of Appeals that the DEA agents had reasonable suspicion for the stop, the Government seeks reversal here by arguing for the first time that no “seizure” occurred, an argument that Mr. Justice STEWART now accepts, thereby pretermitting the question whether there was reasonable suspicion to stop Ms. Mendenhall. Mr. Justice STEWART’s opinion not only is inconsistent with our usual refusal to reverse judgments on grounds not raised below, but it also addresses a fact-bound question with a totality-of-circumstances assessment that is best left in the first instance to the trial court, particularly since the question was not litigated below and hence we cannot be sure is adequately addressed by the record before us.

Mr. Justice STEWART believes that a “seizure” within the meaning of the Fourth Amendment occurs when an individual’s freedom of movement is restrained by means of physical force or a show of authority. Although it is undisputed that Ms. Mendenhall was not free to leave after the DEA agents stopped her and inspected her identification, Mr. Justice STEWART concludes that she was not “seized” because he finds that, under the totality of the circumstances, a reasonable person would have believed that she was free to leave. While basing this finding on an alleged absence from the record of objective evidence indicating that Ms. Mendenhall was not free to ignore the officer’s inquiries and continue on her way, Mr. Justice STEWART’S opinion brushes off the fact that this asserted evidentiary deficiency may be largely attributable to the fact that the “seizure” question was never raised below. In assessing what the record does reveal, the opinion discounts certain objective factors that would tend to support a “seizure” finding, while relying on contrary factors inconclusive even under its own illustrations of how a “seizure” may be established. Moreover, although Mr. Justice STEWART’S opinion purports to make its “seizure” finding turn on objective factors known to the person accosted, in distinguishing prior decisions holding that investigatory stops constitute “seizures,” it does not rely on differences in the extent to which persons accosted could reasonably believe that they were free to leave. Even if one believes the Government should be permitted to raise the “seizure” question in this Court, the proper course would be to direct a remand to the District Court for an evidentiary hearing on the question, rather than to decide it in the first instance in this Court. . . .


Bloom, Robert M., and Mark S. Brodin. Criminal Procedure: The Constitution and the Police. Frederick, MD: Wolters Kluwer, 2013, 139–187.

Morizane, Satoru. “Initial Encounters Between Police and Citizens: A Comparative Study of the United States and Japan.” Emory International Law Review 13 (1999): 561.

Illinois v. Gates

Citation: 462 U.S. 213.

Issue: Whether courts can rely on an anonymous tip in establishing probable cause to search.

Year of Decision: 1983.

Outcome: An anonymous tip can provide probable cause for the issuance of a warrant.

Author of Opinion: Justice William Rehnquist.

Vote: 6-3.

In drafting the Fourth Amendment prohibition against “unreasonable” searches and seizures, congressional framers sought to protect the citizenry against arbitrary police action. The framers were motivated by colonial history, in particular, the fact that British soldiers routinely used “general warrants” (warrants authorizing general searches of houses rather than limited searches for particular items) to search colonists’ houses from top to bottom. As a result, the Fourth Amendment prohibits “unreasonable searches and seizures.” In addition, it provides that “no Warrants shall issue, but upon probable cause, supported by Oath or [affirmation].”

The probable cause requirement contains two elements: not only must a warrant particularly describe the place to be searched and the things to be seized, but it must be based on probable cause to believe that the searched for items can be found in the place to be searched. In Draper v. United States, 358 U.S. 307 (1959), the Court defined probable cause in the following way: “Probable cause exists when ‘the facts and circumstances within their [the arresting officers’] knowledge and of which they had reasonably trustworthy information [are] sufficient in themselves to warrant a man of reasonable caution in the belief that ‘an offense has been or is being committed.’”

When the police seek a warrant, they frequently do so based on the testimony or affidavits of police officers. However, informants are an integral part of the investigative process and are often relied on by police in their affidavits and testimony. Moreover, the testimony of informants is often used in a “hearsay” way (hearsay being defined as an out-of-court statement offered to prove the truth of the matter asserted in the statement). In criminal and civil trials, the use of hearsay is usually prohibited except when the prosecution can fit the testimony into one of the many exceptions to the hearsay rule. By contrast, in probable cause hearings, hearsay is admissible and usable.

A pair of landmark decisions in the 1960s—Spinelli v. United States (1969) and Aguilar v. Texas (1964)—established that two prerequisites must be satisfied before informant testimony can be considered in the warrant process. First, the warrant application must set forth the “underlying circumstances” necessary to enable the magistrate independently to judge the validity of the informant’s conclusions. Second, the application must demonstrate that the informant is “credible” or his information “reliable.” In Aguilar, a search warrant was deemed inadequate because it was based upon an affidavit of police officers who swore only that they had “received reliable information from a credible person and [did] believe” that narcotics were being illegally stored on the described premises. The Court concluded that the officer was required to provide the basis for his conclusions.

Illinois v. Gates is important because the Court concludes that the Aguilar-Spinelli test need no longer be regarded as a precondition to the admissibility of informant testimony in the warrant process. In Gates, the Bloomingdale, Illinois, Police Department received an anonymous handwritten letter suggesting that the Gates were selling illegal drugs out of their Illinois home. The tip went on to state that the Gates would travel to Florida in a few days, and it gave a modus operandi: the wife would drive the car to Florida, the husband would fly to Florida to drive the car back, and the wife would fly back to Illinois on her own. The tip promised that “I guarantee if you watch them carefully you will make a big catch. They are friends with some big drug dealers, who visit their house often.” The police investigated and determined that Mrs. Gates drove the family car to Florida, and Mr. Gates flew down to meet her. However, the Gates deviated from the modus operandi because the two of them drove back toward Illinois together. As soon as the Gates starting heading North, an Illinois magistrate issued a warrant authorizing a search of the Gateses’ car and residence.

In upholding the warrant, the United States Supreme Court reevaluated the Aguilar-Spinelli test. Since the letter was anonymous, it provided virtually nothing from which one might conclude that its author was either honest or his information reliable. In addition, the letter failed to give the “basis for the writer’s predictions regarding the Gates’ criminal activities.” As a result, if the Aguilar-Spinelli test were strictly applied, the trial court would not have had probable cause to issue the warrant.

Instead of summarily rejecting the tip, the Court abandoned the Aguilar-Spinelli test as a precondition to consideration of the tip. The Court emphasized that the probable cause standard is a “practical, nontechnical conception” that focuses on “the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.” Since informants’ tips vary dramatically, the Court doubted that it should apply a single rule to all tips and chose instead to apply a “totality of the circumstances” test. Under that approach, while an informant’s “veracity,” “reliability,” and “basis of knowledge” should be considered in determining the value of a tip, the Court was unwilling to conclude that the Aguilar-Spinelli factors should be regarded as “entirely separate and independent requirements to be rigidly exacted in every case.”

Instead, the Court held that “they should be understood simply as closely intertwined issues that may usefully illuminate the commonsense, practical question whether there is ‘probable cause’ to believe that contraband or evidence is located in a particular place.” In other words, the “two-pronged test” should be transformed into relevant considerations to be used in the totality of circumstances analysis. In other words, “a deficiency in one [prong] 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.”

Applying the “totality of circumstances” test to the Gates facts, the Court held that the magistrate had probable cause to issue the warrant. The Court acknowledged that the tip did not contain information regarding the informant’s identity, and therefore his credibility, and did not contain information suggesting how he came by the information. Nevertheless, the tip included not only allegations regarding the Gateses’ past conduct, but also predictions regarding their future conduct. In particular, the tip referred to the Gateses’ plans to travel to Florida on a specific date in the near future. The Court concluded that the tips’ accuracy regarding the Gateses’ future actions suggested that their other allegations of drug activity were probably accurate as well: “If the informant had access to accurate information of this type a magistrate could properly conclude that it was not unlikely that he also had access to reliable information of the Gateses’ alleged illegal activities.” The Court concluded that probable cause does not require certainty and that “there was a fair probability that the writer of the anonymous letter had obtained his entire story either from the Gates or someone they trusted.”

Justice White, concurring in the judgment, would have upheld the warrant under the Aguilar-Spinelli framework and objected to the majority’s modification of that framework. While he agreed that some lower courts were applying Aguilar-Spinelli “in an unduly rigid manner,” he felt that the better approach was to clarify the meaning and application of the Aguilar-Spinelli test.

Justice William Brennan, joined by Justice Thurgood Marshall, dissented, arguing that the Aguilar-Spinelli test serves a useful purpose because it provides crucial information regarding the informant, helps structure a magistrate’s probable cause inquiry, and therefore produces greater accuracy. Even if a magistrate cannot rely on a tip because he is unable to conclude that the tip “has been obtained in a reliable way by a credible person,” the magistrate can still consider the remaining facts and decide whether probable cause exists. Justice John Paul Stevens, joined by Justice Brennan, also dissented. He doubted that, even considering the evidence under a totality of circumstances test, the magistrate had “probable cause” to believe that the Gates were in possession of illegal drugs.

Gates is an important decision because it redefines the probable cause determination by altering the Aguilar-Spinelli test. Under Gates, in order to rely on a tip, the police need not show that the informant was “credible” and need not provide information suggesting that the information was reliably obtained. Instead, trial courts and magistrates should apply a “totality of circumstances” test and simply consider the Aguilar-Spinelli factors as part of that test.


Justice William Rehnquist Delivered the Opinion of the Court:

. . . This totality-of-the-circumstances approach is far more consistent with our prior treatment of probable cause than is any rigid demand that specific “tests” be satisfied by every informant’s tip. Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a “practical, nontechnical conception.” “In dealing with probable cause, . . . as the very name implies, we deal with probabilities. These are not technical; they are the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.” Our observation in United States v. Cortez, regarding “particularized suspicion,” is also applicable to the probable cause standard:

The process does not deal with hard certainties, but with probabilities. Long before the law of probabilities was articulated as such, practical people formulated certain common-sense conclusions about human behavior; jurors as factfinders are permitted to do the same—and so are law enforcement officers. Finally, the evidence thus collected must be seen and weighed not in terms of library analysis by scholars, but as understood by those versed in the field of law enforcement.

As these comments illustrate, probable cause is a fluid concept—turning on the assessment of probabilities in particular factual contexts—not readily, or even usefully, reduced to a neat set of legal rules. Informants’ tips doubtless come in many shapes and sizes from many different types of persons. . . .

Moreover, the “two-pronged test” directs analysis into two largely independent channels—the informant’s “veracity” or “reliability” and his “basis of knowledge.” There are persuasive arguments against according these two elements such independent status. Instead, they are better understood as relevant considerations in the totality-of-the-circumstances analysis that traditionally has guided probable cause determinations: 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.

If, for example, a particular informant is known for the unusual reliability of his predictions of certain types of criminal activities in a locality, his failure, in a particular case, to thoroughly set forth the basis of his knowledge surely should not serve as an absolute bar to a finding of probable cause based on his tip. Likewise, if an unquestionably honest citizen comes forward with a report of criminal activity—which if fabricated would subject him to criminal liability—we have found rigorous scrutiny of the basis of his knowledge unnecessary. Conversely, even if we entertain some doubt as to an informant’s motives, his explicit and detailed description of alleged wrongdoing, along with a statement that the event was observed first-hand, entitles his tip to greater weight than might otherwise be the case. Unlike a totality-of-the-circumstances analysis, which permits a balanced assessment of the relative weights of all the various indicia of reliability (and unreliability) attending an informant’s tip, the “two-pronged test” has encouraged an excessively technical dissection of informants’ tips, with undue attention being focused on isolated issues that cannot sensibly be divorced from the other facts presented to the magistrate. . . .

For all these reasons, we conclude that it is wiser to abandon the “two-pronged test” established by our decisions in Aguilar and Spinelli. In its place we reaffirm the totality-of-the-circumstances analysis that traditionally has informed probable cause determinations. The task of the issuing magistrate is simply to make a practical, common-sense 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. And the duty of a reviewing court is simply to ensure that the magistrate had a “substantial basis for . . . conclud[ing]” that probable cause existed. We are convinced that this flexible, easily applied standard will better achieve the accommodation of public and private interests that the Fourth Amendment requires than does the approach that has developed from Aguilar and Spinelli. . . .

Our decisions applying the totality-of-the-circumstances analysis outlined above have consistently recognized the value of corroboration of details of an informant’s tip by independent police work. In Jones v. United States we held that an affidavit relying on hearsay “is not to be deemed insufficient on that score, so long as a substantial basis for crediting the hearsay is presented.” We went on to say that even in making a warrantless arrest an officer “may rely upon information received through an informant, rather than upon his direct observations, so long as the informant’s statement is reasonably corroborated by other matters within the officer’s knowledge.” Likewise, we recognized the probative value of corroborative efforts of police officials in Aguilar —the source of the “two-pronged test”—by observing that if the police had made some effort to corroborate the informant’s report at issue, “an entirely different case” would have been presented.

The showing of probable cause in the present case was fully as compelling as that in Draper. Even standing alone, the facts obtained through the independent investigation of Mader and the DEA at least suggested that the Gates were involved in drug trafficking. In addition to being a popular vacation site, Florida is well-known as a source of narcotics and other illegal drugs. Lance Gates’ flight to Palm Beach, his brief, overnight stay in a motel, and apparent immediate return north to Chicago in the family car, conveniently awaiting him in West Palm Beach, is as suggestive of a pre-arranged drug run, as it is of an ordinary vacation trip.

In addition, the magistrate could rely on the anonymous letter, which had been corroborated in major part by Mader’s efforts—just as had occurred in Draper. The Supreme Court of Illinois reasoned that Draper involved an informant who had given reliable information on previous occasions, while the honesty and reliability of the anonymous informant in this case were unknown to the Bloomingdale police. While this distinction might be an apt one at the time the police department received the anonymous letter, it became far less significant after Mader’s independent investigative work occurred. The corroboration of the letter’s predictions that the Gates’ car would be in Florida, that Lance Gates would fly to Florida in the next day or so, and that he would drive the car north toward Bloomingdale all indicated, albeit not with certainty, that the informant’s other assertions also were true. “Because an informant is right about some things, he is more probably right about other facts,”—including the claim regarding the Gates’ illegal activity. This may well not be the type of “reliability” or “veracity” necessary to satisfy some views of the “veracity prong” of Spinelli, but we think it suffices for the practical, common-sense judgment called for in making a probable cause determination. It is enough, for purposes of assessing probable cause, that “corroboration through other sources of information reduced the chances of a reckless or prevaricating tale,” thus providing “a substantial basis for crediting the hearsay.”

Finally, the anonymous letter contained a range of details relating not just to easily obtained facts and conditions existing at the time of the tip, but to future actions of third parties ordinarily not easily predicted. The letter writer’s accurate information as to the travel plans of each of the Gates was of a character likely obtained only from the Gates themselves, or from someone familiar with their not entirely ordinary travel plans. If the informant had access to accurate information of this type a magistrate could properly conclude that it was not unlikely that he also had access to reliable information of the Gates’ alleged illegal activities. Of course, the Gates’ travel plans might have been learned from a talkative neighbor or travel agent; under the “two-pronged test” developed from Spinelli, the character of the details in the anonymous letter might well not permit a sufficiently clear inference regarding the letter writer’s “basis of knowledge.” But, as discussed previously, probable cause does not demand the certainty we associate with formal trials. It is enough that there was a fair probability that the writer of the anonymous letter had obtained his entire story either from the Gates or someone they trusted. And corroboration of major portions of the letter’s predictions provides just this probability. It is apparent, therefore, that the judge issuing the warrant had a “substantial basis for . . . conclud[ing]” that probable cause to search the Gates’ home and car existed. The judgment of the Supreme Court of Illinois therefore must be Reversed.

Justice STEVENS, with whom Justice BRENNAN joins, dissenting.

The fact that Lance and Sue Gates made a 22-hour nonstop drive from West Palm Beach, Florida, to Bloomingdale, Illinois, only a few hours after Lance had flown to Florida provided persuasive evidence that they were engaged in illicit activity. That fact, however, was not known to the magistrate when he issued the warrant to search their home.

What the magistrate did know at that time was that the anonymous informant had not been completely accurate in his or her predictions. The informant had indicated that “Sue drives their car to Florida where she leaves it to be loaded up with drugs. . . . Sue flies back after she drops the car off in Florida.” Yet Detective Mader’s affidavit reported that she “left the West Palm Beach area driving the Mercury northbound.”

The discrepancy between the informant’s predictions and the facts known to Detective Mader is significant for three reasons. First, it cast doubt on the informant’s hypothesis that the Gates already had “over $100,000 worth of drugs in their basement,” The informant had predicted an itinerary that always kept one spouse in Bloomingdale, suggesting that the Gates did not want to leave their home unguarded because something valuable was hidden within. That inference obviously could not be drawn when it was known that the pair was actually together over a thousand miles from home.

Second, the discrepancy made the Gates’ conduct seem substantially less unusual than the informant had predicted it would be. It would have been odd if, as predicted, Sue had driven down to Florida on Wednesday, left the car, and flown right back to Illinois. But the mere facts that Sue was in West Palm Beach with the car, that she was joined by her husband at the Holiday Inn on Friday, and that the couple drove north together the next morning are neither unusual nor probative of criminal activity.

Third, the fact that the anonymous letter contained a material mistake undermines the reasonableness of relying on it as a basis for making a forcible entry into a private home.

Of course, the activities in this case did not stop when the magistrate issued the warrant. The Gates drove all night to Bloomingdale, the officers searched the car and found 400 pounds of marijuana, and then they searched the house. However, none of these subsequent events may be considered in evaluating the warrant, and the search of the house was legal only if the warrant was valid. I cannot accept the Court’s casual conclusion that, before the Gates arrived in Bloomingdale, there was probable cause to justify a valid entry and search of a private home. No one knows who the informant in this case was, or what motivated him or her to write the note. Given that the note’s predictions were faulty in one significant respect, and were corroborated by nothing except ordinary innocent activity, I must surmise that the Court’s evaluation of the warrant’s validity has been colored by subsequent events.

Although the foregoing analysis is determinative as to the house search, the car search raises additional issues because “there is a constitutional difference between houses and cars.” An officer who has probable cause to suspect that a highly movable automobile contains contraband does not need a valid warrant in order to search it. This point was developed in our opinion in United States v. Ross, which was not decided until after the Illinois Supreme Court rendered its decision in this case. Under Ross, the car search may have been valid if the officers had probable cause after the Gates arrived.

In apologizing for its belated realization that we should not have ordered reargument in this case, the Court today shows high regard for the appropriate relationship of this Court to state courts. When the Court discusses the merits, however, it attaches no weight to the conclusions of the Circuit Judge of DuPage County, Illinois, of the three judges of the Second District of the Illinois Appellate Court, or of the five justices of the Illinois Supreme Court, all of whom concluded that the warrant was not based on probable cause. In a fact-bound inquiry of this sort, the judgment of three levels of state courts, all of whom are better able to evaluate the probable reliability of anonymous informants in Bloomingdale, Illinois, than we are, should be entitled to at least a presumption of accuracy. I would simply vacate the judgment of the Illinois Supreme Court and remand the case for reconsideration in the light of our intervening decision in United States v. Ross.


Bloom, Robert M., and Mark S. Brodin. Criminal Procedure: The Constitution and the Police. Frederick, MD: Wolters Kluwer, 2013, 44–67.

Finer, Joel Jay. “Gates, Leon, and the Compromise of Adjudicative Fairness.” Cleveland State Law Review 33 (1984–1985): 707.

United States v. Leon

Citation: 468 U.S. 897.

Issue: Whether the Court should create a “good faith” exception to the exclusionary evidence rule.

Year of Decision: 1984.

Outcome: The Court created a “good faith” exception to the exclusionary evidence rule after balancing the “costs” of exclusion against the “benefits.”

Author of Opinion: Justice Byron White.

Vote: 7-2.

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