An economic analysis of search and seizure law.

• Author: Kerr, Orin S.
• Position: II. An Economic Understanding of Fourth Amendment Rights C. Constitutional Reasonableness: The Warrant Requirement and Its Exceptions through Conclusion, with footnotes, p. 618-647

3. Constitutional Reasonableness: The Warrant Requirement and Its Exceptions

   When the government conducts a search or seizure, the Fourth Amendment requires that it must be "reasonable." The Supreme Court has explained that reasonableness usually requires a search warrant or an exception to the warrant requirement. (142) We can therefore review the doctrines related to reasonableness by starting with the warrant requirement and then reviewing its exceptions. Broadly speaking, the doctrine seems to reflect a general principle that searches and seizures are reasonable when the government can establish specific facts either showing an expected law enforcement benefit, low external costs in context, or some combination of the two.

   1. The Warrant Requirement

      The Fourth Amendment states that "no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." (143) Probable cause requires proof of "a fair probability that contraband or evidence of a crime will be found in a particular place." (144) The particularity requirement limits the scope of Fourth Amendment searches to a particular place and particular evidence. The particularity requirement limits the scope of Fourth Amendment searches to a particular place and particular evidence. The requirement forbids "general searches," which are searches that do not limit where the police can search and for what. (145) Under the particularity requirement, the government can typically search only one home at a time, and the warrant must name the evidence sought to the degree practicable.

      The requirements of probable cause and particularity limit invasive searches to circumstances that are likely to advance investigations and that will have limited external costs. Probable cause suggests a relatively high P; particularity requires a relatively low [C.sub.e]. The warrant requirement allows searches and seizures when the imposition of [C.sub.e]is offset by a significant P and the use of mechanisms to lower [C.sub.e].

      The probable cause requirement serves three roles. First, it requires the government to show a likely benefit that justifies its cost. The government must establish a significant likelihood that the search will be a success and that evidence of the crime will be recovered in the place searched. This will tend to correlate with a high P: the more likely it is that evidence will be found, the more likely the search will assist in solving the case. A "fair probability" (147) that evidence will be found in the place to be searched establishes a significant likelihood that the search will advance the investigation.

      Second, the probable cause requirement channels police resources into low-[C.sub.e] evidence-gathering that can minimize the need for high-[C.sub.e] searches. If the search doctrine accurately distinguishes low-externality techniques from high-externality techniques, the probable cause requirement will limit the number of high-externality searches by forcing the police to use low-externality steps to identify where evidence is likely to be located. If the police can solve cases using only low-externality methods, they will try that first. And if the police need warrants, they will try to gather evidence to justify those warrants using low-externality techniques. The necklace hypothetical discussed earlier in Part I hints at this dynamic. The warrant requirement forced the police to conduct a low-externality investigation to find out which house stored the necklace instead of simply raiding every house.

      Probable cause can also limit [C.sub.e] by increasing the chance that external costs will be borne by the guilty rather than the innocent. A search of a guilty person will generally impose smaller external costs than a search of someone who is innocent. (148)An innocent person who is searched is likely to feel shocked and humiliated by the experience; a guilty person is more likely to feel unlucky that the police were able to catch him. (149) Although a search warrant for evidence of crime can be used to search the home of an innocent third party, (150) the more common case is for a warrant to be executed at the home of a suspect. The requirement of probable cause thus leads to more searches and seizures of the guilty, which will generally be associated with lower [C.sub.e].

      The particularity requirement also lowers [C.sub.e] by ensuring that warrant searches are narrow in location and scope. The search must occur at a specific place, such as an individual home: a warrant cannot be obtained to search a city block or an entire neighborhood. (151) A warrant allowing such a broad search would be a prohibited "general warrant" that would impose an extremely high [C.sub.e]. Requiring that the warrant describe the item to be searched with particularity limits where the police can search (they can only search where the described evidence could be found), how much they can take away (they ordinarily can only seize evidence described in the warrant), and potentially how long the search can continue (as the search must end when the described evidence has been located). (152) The particularity requirement thus limits [C.sub.e] by limiting how much the government can search and how much property it can take away.

   2. Exceptions to the Warrant Requirement

      Fourth Amendment doctrine also recognizes several exceptions to the warrant requirement. Established exceptions include consent, exigent circumstances, as well as the general reasonableness approach that the Supreme Court occasionally applies. (153) In these circumstances, a search is reasonable--and therefore allowable--even if no warrant has been obtained. Each of these exceptions can be explained as allowing investigative steps when external costs Cc are low, the expected benefit P*V is high, or some combination of the two.

      First, consent searches are reasonable when a person with common authority over the space to be searched voluntarily consents to a search of that space. (154) The voluntariness standard is based on all of the circumstances that indicate whether the consent was voluntary or instead the product of duress or coercion. (155) Consent doctrine is generally consistent with an economic perspective to the extent it allows searches when the expected [C.sub.e] should be unusually low. When a person with authority over a space voluntarily consents to a search, the government will not need to surprise the targets by breaking down the door and rifling through property. The consenting person can open the door, so the door is not broken down; she can direct the police to the evidence, so the police do not need to rifle through the entire space. Further, those who consent to a search will not have the same sense of violation or humiliation that they would have if the police were to raid their spaces without permission. If the consent is truly voluntary--a significant assumption--the consenting individual is in charge and external costs should be comparatively low.

      The police can also conduct a warrantless search or seizure when justified by exigent circumstances. This exception applies when, based on the totality of the circumstances, "the exigencies of the situation make the needs of law enforcement so compelling that a warrantless search is objectively reasonable under the Fourth Amendment." (156) This can occur in several different circumstances. In some cases, exigent circumstances allow searches when the trail would otherwise go cold: the entry may be necessary "to prevent the imminent destruction of evidence," (157) or when the officers are in "hot pursuit of a fleeing suspect." (158) In those circumstances, most courts require probable cause in addition to the emergency. (159) Exigent circumstances searches may also be justified when the officers have a quick opportunity to prevent harms, such as when officers enter "to provide emergency assistance to an occupant of a home." (160)

      In general, the exigent circumstances doctrine allows searches when the benefit P*V is unusually high. Consider Welsh v. Wisconsin. (161) A suspected drunk driver wandered into his home, and a police officer entered the home without a warrant to arrest the suspect in his bedroom. The Court ruled that the exigent circumstances doctrine did not allow the entry. (162) On one hand, entry into a home was the "chief evil" that the Fourth Amendment protected against, suggesting that the costs [C.sub.e] was high. (163) On the other hand, the crime of drunk driving was only a very minor offense--under Wisconsin law at the time, it was only a noncriminal violation--indicating a very low interest of the state (and thus a low F). (164) Given the significance of entering the home, forced entry to gain evidence of a crime that was of such minor significance to the state was not reasonable. (165)

      Fourth Amendment doctrine also permits the police to engage in several kinds of searches justified by officer safety. During a temporary stop, officers can frisk a suspect for weapons if there are specific and articulable facts that a suspect is armed and dangerous. (166) After making an arrest, they can search neighboring areas that might harbor a co-conspirator. (167) During a traffic stop, officers can order the driver and passengers out of the car. (168) All of these steps involve relatively narrow searches and seizures justified as measures that protect officer safety and thereby lower internal costs [C.sub.i]. If an officer cannot take steps to avoid danger, he increases the chances of incurring the severe costs of being seriously injured or even killed. If a search or seizure for officer protection is only minimally invasive--that is, it has low [C.sub.e]--then allowing an officer to take such a modest step to avoid this severe potential cost will lower the overall cost of enforcing the law.

      Finally, the Supreme Court has...