Search and Seizure

Search and seizure law today is built around three key questions. First, did the police "search" or "seize" anyone or anything? If not, the law leaves police action basically unregulated. If so, what justification must the police have—probable cause, reasonable suspicion, or (in rare cases) something else? Finally, what process must the police follow—must they seek permission in advance from a magistrate, or can they search first and defend themselves in a suppression hearing later?

The definition of "search" and "seizure." The most important of these questions may be the first one, for if a given police tactic is not a "search" or "seizure" within the meaning of the Fourth Amendment, the police are free to use that tactic when and on whom they wish, free of legal constraint.

"Searches," in Fourth Amendment law, are police tactics that infringe a "reasonable expectation of privacy." A reasonable expectation of privacy is the kind of expectation any citizen might have with respect to any other citizen. A fair translation of this standard might go as follows: Police can see and hear the things that any member of the public might see and hear, without fear of Fourth Amendment regulation. Only when police cross that line, only when they see and hear things that members of the public would not be allowed to see and hear, has a "search" taken place.

A few examples might clarify the standard. Eavesdropping on telephone conversations is a "search." Overhearing a conversation on the street is not. Climbing over a backyard fence is a "search." Observing the same backyard from the window of an airplane is not. Hiding in the bushes outside a house and looking inside is a "search." Standing on a public street and looking through open curtains into a living room is not. Opening a briefcase to inspect its contents is a "search." Observing someone carrying a briefcase on the street is not.

When applying the reasonable-expectationof-privacy standard, courts ask whether, at the moment the police officer observed the illegal behavior, he was in a position any member of the public might have been in. The duration and intensity of police observation does not matter. Thus, police officers can stake out a private home, taking up residence across the street and watching all comings and goings for a period of days or even weeks, and that behavior does not constitute a "search," because at any given moment, any member of the public might have been looking. And police can follow a suspect's movements along public streets, in shops or restaurants, and so forth; once again, such behavior is not a "search" (even though it amounts to something like stalking), because any member of the public might have seen any given transaction in public.

One other feature of the definition of "search" bears mention. Consensual transactions are not "searches," even if consent was given under false pretenses. So if a police officer poses as a drug buyer, and a suspect lets him into the suspect's house in order to sell him drugs, anything the officer sees and hears in the house is fair game—no Fourth Amendment "search" has taken place. The use of undercover agents is thus routinely permitted by search and seizure law, whether or not the police have good reason to suspect the person with whom the undercover agent is dealing of any crime. Also, if a police officer asks permission to look in a suspect's car or briefcase, and the suspect says yes, once again no "search" has taken place. This last point is particularly important. Police officers exert a certain amount of force just by virtue of their status. For many, perhaps most, a request from a police officer will sound like a command; the tendency will be to say yes whether one wants to or not. Nevertheless, if the police officer asks, and the suspect says yes, that almost always amounts to consent. Only if the officer behaves unusually coercively—if he pulls his weapon, or grabs hold of the suspect, or the like—will a court find that the consent was involuntary.

All these rules sound complicated; in practice, they are relatively simple. In general, the police are "searching" when they are either committing some kind of trespass—grabbing a suspect's briefcase and looking inside, breaking into a house or apartment, climbing over a backyard fence—or are engaged in some kind of electronic eavesdropping—for example, wiretapping a phone. Most of the rest of what police do to gather information falls outside the Fourth Amendment.

"Seizures" are harder to define. The Supreme Court says that a suspect has been "seized" if a reasonable person in the suspect's shoes would not feel free to leave. If the Court took its own language seriously, every conversation between a police officer and a citizen would be a "seizure." After all, few people, when approached on the street by an officer, feel free to turn on their heels and walk away. The consequences of that position would be huge; the police would need some adequate justification for every interaction.

Not surprisingly, the law does not operate that way in practice. The working standard seems to be roughly the same as the standard for consent. The dispositive question is this: Did the police officer behave coercively (not counting the coercion that is inherent in a police officer questioning a suspect)? If so, the encounter is a "seizure." If not, it is not. Compared to the definition of "search," which has acquired a good deal of definition over the years, the definition of "seizure" remains remarkably vague and open-ended. Conversations on the street between police officers and citizens often begin as consensual conversations; at some point the encounter often becomes a "seizure." Neither the officer nor the suspect—nor, for that matter, courts—know precisely when that point is.

Probable cause and reasonable suspicion. When the police have searched or seized someone, the Fourth Amendment requires some justification. With rare exceptions, the justification takes one of two forms: either the police must have probable cause, or they must have reasonable suspicion. The following paragraphs explain what these standards mean, and to what cases each standard applies.

Probable cause has never received a clear definition in the cases; the Supreme Court has said, unhelpfully, that an officer has probable cause to arrest when "the facts and circumstances within [the 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" Brinegar v. United States, 338 U.S. 160, 175–76 (1949). What that means in practice seems to be, roughly, more likely than not. Thus, probable cause to arrest requires enough information to show that the suspect probably committed the crime. Probable cause to search requires enough information to show that evidence of crime can probably be found in the place to be searched.

One issue that regularly arises in the cases is whether police can rely on tips from informants to establish probable cause. Informants are sometimes ordinary citizens who call into police stations with useful information; more commonly they are criminals themselves who report information about other criminals in return for some favors—sometimes leniency, sometimes cash—from the police. Informants are common in police work, and especially in the policing of drug markets. (The leading study of search warrants shows that jurisdictions with the most drug cases also make the most use of informants' tips.) Such tips are clearly useful to the police; they equally clearly pose significant problems. Informants may have some incentive to frame rivals, or to concoct whatever information will get them the greatest reward from the police. And since the identity of the informant is almost always confidential—for obvious reasons, informants tend to insist on anonymity—there is some risk that police will make up phony informants to justify their own hunches. For these reasons, the Supreme Court in the 1960s and 1970s placed serious restrictions on the use of informants' tips to generate probable cause.

Those restrictions were largely removed in 1983, in Illinois v. Gates, 462 U.S. 213 (1983). The Court in Gates held, basically, that informants' tips were to be treated like any other information. And the Court specifically approved findings of probable cause where an informant's tip is partially corroborated—as where the informant says a suspect will be driving a certain car at a certain time and place and will be carrying drugs, and the officer confirms that the suspect was indeed driving that car at that time and place.

Like probable cause, reasonable suspicion is not well defined in the cases. Indeed, the only thing one can confidently say about it is that reasonable suspicion means something less than probable cause. Just how much less is unclear. A good indication of the kind and level of information required is the following common fact pattern. A police officer, on foot or in his car, turns a corner on a city street in an area known as a locale for drug trafficking. A young man standing on a street corner sees the officer, turns, and runs in the other direction. The officer knows nothing about the young man other than that he was in a place where crime was common, and that he ran when he saw the police. Does the officer have reasonable suspicion?

In Illinois v. Wardlow, 120 S.Ct. 673 (2000), the Supreme Court said the answer is yes. Likewise, if police see a suspect in a place where drugs are often sold, and if the suspect has a series of brief conversations with people the police know to be drug users, most courts would say the police have reasonable suspicion. In these cases the police have some ground for suspecting criminality, but not a great deal. Reasonable suspicion is meant to capture that intermediate condition.

To what cases do these standards apply? Probable cause is the governing standard for arrests, and for searches of homes, cars, or personal effects. For arrests, the standard is probable cause to believe the suspect has committed a crime; for searches it is, with one important exception, probable cause to believe evidence will be found in the place sought. The exception is for searches "incident to arrest." When the police make a valid arrest, they are permitted to search the suspect's person, any belongings he has with him, and his car; if the arrest occurs at home, they may search the area within his immediate control. These searches incident to arrest are legal if the arrest is legal. Thus, probable cause to arrest authorizes not only arrests but also a good many searches.

Reasonable suspicion is the governing standard for brief stops, as where an officer detains a pedestrian for a few minutes or pulls over a car in order to ask the driver a few questions. Reasonable suspicion of the presence of a weapon is the standard for very brief searches, such as a pat-down or frisk of a suspect's outer clothing. In practice, reasonable suspicion of the presence of a weapon tends to follow from reasonable suspicion of criminal activity. At least for serious crimes, judges tend to find that suspicion of the crime entitles the police to frisk the suspect in order to detect any weapons. The officer is, of course, entitled to check the contents of the pockets if this frisk turns up anything that might be a weapon. Naturally, the line between lumps that might be weapons and lumps that might be evidence of crime (drugs, for example) is a fine one. As a result, frisks for weapons tend to turn into frisks for either weapons or evidence.

The authority to frisk, or conduct a brief search, based on reasonable suspicion extends beyond the suspect's clothing. If the suspect is in a car, the officer is entitled to briefly look through the car's interior. If the suspect is carrying a purse or briefcase, the officer can briefly look inside, long enough to ensure that it does not contain a gun. And any evidence the officer finds during the course of such inspections is admissible.

Thus, given reasonable suspicion, officers can briefly detain pedestrians or pull over drivers of cars. Given reasonable suspicion of the kind of crime often associated with weapons, officers can briefly look around the car's interior, frisk a suspect's outer clothing, and open any containers (such as a purse or bag) that the suspect might reach to check for weapons. More extensive searches and seizures require probable cause.

Special cases—police use of force and group seizures. There remain two important categories of cases where neither probable cause nor reasonable suspicion applies. The first is police use of force, where the standard is higher than probable cause. The second is group seizures such as roadblocks, where the standard is lower than reasonable suspicion.

At common law, the police could use whatever force necessary to apprehend suspects and to bring them under control. If suspected of a felony, and if he fled, the suspect could be killed. These doctrines were still in force as late as the 1980s; not until 1985 did the Supreme Court decide that a higher standard was required for police use of force against suspects.

In that case, Tennessee v. Garner, 471 U.S. 1 (1985), the police shot and killed a fleeing burglary suspect; there was no reason to believe the suspect was armed or had threatened serious physical harm to anyone. The Court concluded that the shooting was unreasonable, and hence violated the Fourth Amendment. The Court ruled that deadly force was permissible only given some immediate danger of death or serious physical injury. Immediate danger is presumed if the police have probable cause to believe the suspect has caused or threatened death or serious injury, and if the suspect has been warned to stop but refuses to do so. The standard for using nondeadly force is both less demanding and less certain: the Supreme Court says only that officers must behave reasonably, taking account of the danger the suspect poses, the kind of crime he is suspected of committing, and the amount of force necessary to bring him under control.

These standards governing police use of force receive much less attention in the courts than the standards governing police frisks or house searches, because use-of-force claims are litigated much less frequently. The reason has to do with remedies. The primary remedy for Fourth Amendment violations is the exclusionary rule; the huge majority of Fourth Amendment claims arise as efforts by criminal defendants to suppress illegally obtained evidence. But when police beat or shoot a suspect, they are not looking for evidence. Thus, excessive force claims only rarely lead to efforts to suppress evidence; the exclusionary rule is essentially irrelevant to these claims.

Instead, excessive force claims arise either as claims for damages by the victim (or the victim's next-of-kin), or as criminal prosecutions of the offending officers. The latter happen only very rarely. Damages claims are more frequent, but still amount to a very small fraction of the number of exclusionary rule claims. Which explains why the law of excessive force is so much less developed than, say, the law of car searches or street stops.

Group searches and seizures are the second category of cases that fall outside the probable cause and reasonable suspicion standards. Here the law is both complex and unclear. In United States v. Martinez-Fuerte, 428 U.S. 543 (1976), the Supreme Court permitted the use of highway checkpoints near the border to check for illegal immigrants; at these checkpoints all cars were stopped and all drivers seized, even though the government had no reason to suspect any particular driver of harboring illegal aliens. Similarly, in Michigan Highway Department v. Sitz, 496 U.S. 444 (1990), the Court ruled that officers may set up roadblocks to catch drunk drivers, even though the officers have no ground for suspecting any particular driver of any wrongdoing. But in Indianapolis v. Edmond, 121 S.Ct. 447 (2000), the Court barred the use of roadblocks designed to catch drug violators. For now, the government can apparently seize (and perhaps search) all members of a group in pursuit of goals other than ordinary criminal law enforcement (border control in Martinez-Fuente, highway safety in Sitz). But it cannot use power as a routine crime control tactic.

Drugs may fall on either side of this boundary. In Edmond, drug checkpoints were banned. But the result has been different in a number of cases involving drug testing. Government agencies sometimes seek to require periodic testing of employees, without any showing that any given employee was reasonably suspected of drug use or other misconduct. These testing programs have sometimes prevailed in the courts and sometimes not; the usual approach is to ask whether there is some "special need" to test the category of employees in question. The idea is similar to the idea behind Martinez-Fuerte and Sitz: In support of these testing programs, the government often claims suspicionless testing is permissible as long as many people are tested; that is, as long as no one person is singled out. If that argument were applied to tactics like group fingerprinting or DNA testing, it would considerably expand the scope of police authority. For now, Edmond is holding the line against such an expansion. But the line is unstable. The government can argue, with some force, that its interest in fighting drug crime is at least as strong as its interest in catching drunk drivers. If so, it seems odd that the police would be granted substantially greater power in the latter setting than in the former.

The role of substantive law. Probable cause and reasonable suspicion both refer to a level of probability, a likelihood that some asserted fact—the suspect committed a crime, or evidence of crime will be found in a particular place—is true. The asserted fact always involves crime. It follows that the meaning of probable cause or reasonable suspicion depends on what counts as a crime. To put it another way, to say that the police have probable cause to arrest a given suspect is to say they have reason to believe that the suspect probably violated some criminal statute. Whether the claim is right depends in part on just what behavior criminal statutes forbid. If enough criminal statutes forbid enough conduct, the police will have probable cause to arrest a large portion of the population.

Something much like this was true before the late 1960s. Loitering statutes made it a crime to hang around on street corners; vagrancy statutes made it a crime to be able-bodied but unemployed, or to be a "rogue" or "vagabond." These open-ended prohibitions plausibly covered a large fraction of ordinary street behavior, at least by people the police might wish to arrest or search. Consequently, the police had something close to blanket authority to arrest or search a large portion of the population. The probable cause standard mattered little.

In the late 1960s and early 1970s, most loitering and vagrancy statutes were declared unconstitutional on the ground that they were unacceptably vague. States and cities responded with a wave of statutes and ordinances criminalizing loitering with intent to commit acts of prostitution or drug use; some jurisdictions went farther, passing laws forbidding loitering in the presence of members of gangs that themselves were involved in various sorts of criminal activity. In Chicago v. Morales, 119 S.Ct. 1849 (1999), the Supreme Court struck down one such law, declaring that it was, like older loitering and vagrancy laws, too vague, and that it infringed on individuals' liberty to wander about on public streets free of official interference.

Morales was not a Fourth Amendment decision; the Court relied on the due process clause of the Fourteenth Amendment instead. But the Court's decision may have a large impact on the scope of Fourth Amendment protection. Again, if "crime" covers enough territory, police will have reasonable suspicion or probable cause with respect to most people, and Fourth Amendment standards will, as a practical matter, cease to operate. Morales may suggest that, at least with respect to pedestrians, the Court will not permit that state of affairs to recur.

The story is different when it comes to automobile traffic. In many states, moving violations—speeding, changing lanes without using a turn signal, running a stop sign, and the like—are, technically, crimes. Since such rules are not strictly enforced in most places (to the extent that speeding is the norm on many roads), most drivers are, technically, committing crimes most of the time, which gives the police authority to stop a large fraction of drivers.

That authority can be exercised strategically. If police believe a given suspect is transporting drugs, but they lack the kind of support needed to satisfy the probable cause or reasonable suspicion standards, they can wait for the suspect to run a stop sign, or speed, or violate some other traffic regulation, then pull the suspect over, arrest him for the traffic offense, and search him and his car incident to the arrest—all the while looking for drugs. In Whren v. United States, 517 U.S. 806 (1996), the Supreme Court held that this sort of pretextual police search is permissible. As long as the police have probable cause to believe the suspect is doing something the state defines as a crime, an arrest is legal, and if an arrest is legal, so is a search incident to arrest.

Whren and Morales are thus in some tension. Whren gives police near-blanket authority to stop vehicles; Morales seems to forbid near-blanket authority to stop pedestrians. In both cases, the primary determinant of the scope of police authority is not Fourth Amendment law, but the law that defines crimes.

The warrant requirement. All police searches and seizures are subject to legal challenge, but the challenge ordinarily comes after the fact. The officer searches, the defendant moves to suppress evidence found in the search, and the court holds a hearing to determine whether the search was legal. Where a search or arrest warrant is required, by contrast, judicial evaluation of the search or arrest happens in advance. The officer fills out a brief warrant application, with a sworn affidavit stating the facts in support of the application; a magistrate reviews the application, sometimes questioning the officer, and then decides whether to issue the warrant. If the warrant is issued and the search turns up evidence, the defendant can still seek to suppress it, but the court will give substantial deference to the magistrate's judgment. Thus, Fourth Amendment law knows two procedures for testing the legality of a search: the warrant process before the search, and the suppression hearing after.

In form, the law requires the first of these procedures—warrants—unless some special exception applies. In practice, the exceptions swallow the rule. Warrants are not required for (among other things) arrests outside the suspect's home, searches incident to arrest (which, remember, cover the suspect's clothing, car, and belongings at the time of arrest), searches of cars whether or not anyone is arrested, and brief stops or frisks of suspects. These categories encompass the large majority of searches and seizures.

Warrants are required for wiretaps, for searches of homes, and for arrests that take place in a home. Even here, there is an exception for cases where "exigent circumstances" exist—where getting a warrant is impractical because of the danger that suspects will flee or evidence will be destroyed.

The warrant requirement thus applies chiefly when police wish to enter a private home. Elsewhere, police generally are allowed to search first, and face judicial scrutiny afterward. Fourth Amendment law purports to have a warrant requirement with a few narrow exceptions. The true rule is no warrant requirement, with an exception for homes and wiretaps.

In theory, this regime offers an extra measure of protection for house searches. Forcing police to ask permission in advance of a search, and requiring that permission come from a neutral magistrate, should weed out potential searches based on thinly supported police hunches. In practice, it is unclear how much the warrant requirement accomplishes. Most reviews of warrant applications are cursory, and magistrates only hear from one side—the police officer. Not surprisingly, most applications are granted. That, one might think, suggests warrants are something of a sham, a process by which discretionary decisions by police officers are rubber-stamped by magistrates. On the other hand, the leading study of the warrant process suggests the large majority of searches pursuant to warrants turn up evidence of crime. That, one might suppose, suggests warrants work, that they serve as an effective screen. The truth may be somewhere in between these two views, or it may be different in different jurisdictions.