§ 4.02. Justification for Encounters

(a) Absent state or federal law to the contrary, an officer may, in any location in which the officer is lawfully present:

  • (1) conduct an initial encounter with an individual without any suspicion that the individual is involved in or has evidence of a crime;
  • (2) conduct a stop of an individual based on reasonable suspicion to believe that the individual is involved in or has evidence of unlawful conduct;
  • (3) issue a summons or a citation to an individual based on probable cause that the individual has engaged in unlawful conduct; and
  • (4) conduct a custodial arrest of an individual based on probable cause that the individual has committed a felony or a misdemeanor, so long as an arrest is permitted under state law.

(b) Agencies should ensure that officers exercise this authority consistent with §§ 4.03 to 4.07.

(c) Encounters that would not be permissible under this Section because officers lack the required level of suspicion should not occur at all, unless they are conducted consistent with the requirements of Chapter 5, dealing with suspicionless searches and seizures.


a. Generally. This Section describes the minimum level of suspicion or cause that an officer must have in order to initiate an encounter, conduct a stop, issue a summons, or make an arrest. It largely tracks what courts have said are the threshold constitutional requirements for those actions. However, just because officers may conduct a stop or an arrest does not mean that doing so is appropriate or consistent with the goals of public safety. Section 4.03 sets out additional factors that agencies should consider in providing guidance to officers on whether any of these actions are appropriate in a given case.

b. Initial encounters. As a matter of federal constitutional law, an officer may approach an individual for any reason so long as the officer does nothing to impede the individual’s freedom to leave or otherwise terminate the encounter—and so long as a reasonable person would feel free to walk away or otherwise terminate the encounter. These Principles accept that understanding, recognizing nonetheless that there is a degree of fiction in the claim that individuals do indeed feel free to leave or terminate encounters with the police. Some jurisdictions have imposed additional requirements on initial encounters—New York, for example, requires that officers have an “objective, credible reason” to approach a person on the street—these Principles do not go that route. Experience suggests that such requirements are both difficult to enforce and largely ineffective in addressing the concerns with the officer-initiated encounters described throughout this Chapter. Instead, it is important for agencies, consistent with § 4.03, to provide guidance and training to officers as to when these sorts of encounters are appropriate, as well as how they should be conducted to minimize the risk of undermining legitimacy and trust.

c. Stops based on reasonable suspicion. This Section adopts the standard first announced in Terry v. Ohio, 88 S. Ct. 1868 (1968), that a police officer may briefly detain a person or vehicle if the officer has reasonable suspicion to believe that the target of the stop is involved in or has evidence of criminal activity. Reasonable suspicion is more than a hunch. Officers must be able to narrate the reasons for their suspicion. Neither race, nor any other protected status, such as gender identity, should be used as a basis for reasonable suspicion to justify a Terry stop, unless the characteristic is part of a specific suspect description that includes substantially more information than the person’s race or protected status.

Agencies also should consider requiring officers to articulate the specific offense that they believe has occurred or is about to occur. Although in Terry itself the officer was able to specify clearly the crime in question, courts since have upheld stops based on more generalized suspicion of criminal activity—for example, flight from an officer in a high-crime area. Even if legally permissible, these sorts of stops should be discouraged. Studies suggest that stops based on vague or generalized criteria are less likely to lead to arrest or to turn up any evidence of criminal activity, and therefore may result in unnecessary intrusions. There also is evidence to suggest that when officers rely on such criteria, racially discriminatory and class-based effects emerge.

A stop based on reasonable suspicion must be brief, typically no longer than 20 minutes, and must be limited in scope to investigating the offense that the officer suspects and can articulate, unless during the course of the stop the officer develops reasonable suspicion to believe that another offense has occurred or is about to occur. A stop that exceeds the scope or duration permitted on the basis of reasonable suspicion becomes a de facto arrest, and is unlawful absent probable cause to support it.

Whenever possible, the grounds for the stop should be memorialized in some fashion, preferably prior to the stop. Many officers today wear body cameras, which typically must be turned on before such stops. It should be a simple matter for the officer to state—when time permits—the basis for the stop. When time does not permit, the basis for the stop can be recorded on a form pertaining to the stop immediately after the fact. In addition, principles of procedural justice require that, absent some public-safety reason to the contrary, officers inform individuals why they are being stopped at some point during the encounter.

d. Past crimes as a basis for reasonable suspicion. Like probable cause, reasonable suspicion has a temporal dimension and may become stale. Although officers may stop an individual based on suspicion of a completed offense, officers must have some basis for thinking that the stop will in fact further an investigation of that offense. For example, if an officer sees a vehicle that previously had been seen leaving the scene of a robbery, an officer may have reasonable suspicion for stopping the vehicle to speak to the driver, even if the robbery occurred several days or weeks earlier. On the other hand, information that someone had been in possession of narcotics or a firearm at some earlier point in time would not justify a stop absent additional reason to believe that the individual currently is in possession of contraband or a weapon.

e. Arrests. An arrest is a more serious intrusion than a stop, and must therefore be based on a higher level of suspicion. An arrest must be supported by probable cause that the individual detained has committed a crime or a violation. Probable cause requires that an officer have sufficient facts to cause a reasonably prudent person to think that a crime is being or has been committed. An officer may develop probable cause based on direct observation of potential criminal activity, or based on a credible, corroborated tip from an informant. See also § 12.03. As with stops based on reasonable suspicion, officers should articulate the basis for an arrest as proximate as possible thereto. Given the wide array of criminal offenses for which police have discretion to arrest, an arrest should not occur unless it is necessary to protect the public or to ensure that the person appears in court. See § 4.05.

f. Programmatic seizures. The Principles in this Chapter apply to officer-initiated encounters that are based on suspicion specific to the individual or individuals involved. As discussed in greater detail in Chapter 5, officers also are permitted to search and seize individuals as part of a suspicionless search and seizure program, such as a sobriety checkpoint or airport security. Such programmatic searches and seizures need not be based on individualized suspicion, but must instead be conducted in an evenhanded and nonarbitrary manner, according to a policy that is set out in advance. See § 4.05.

Reporters’ Notes

These Principles generally adopt the basic framework first announced in Terry v. Ohio, 392 U.S. 1 (1968), which recognizes three broad categories of police–citizen encounters: initial encounters, which do not require any suspicion; investigative stops, which must be supported by reasonable suspicion; and arrests, which must be supported by probable cause. As the U.S. Supreme Court explained in Terry, this approach accommodates the fact “that in dealing with the rapidly unfolding and often dangerous situations on city streets the police are in need of an escalating set of flexible responses, graduated in relation to the amount of information they possess.” Id. at 10.

Courts repeatedly have emphasized that although a stop falls short of an arrest, it nevertheless constitutes a significant intrusion, and that officers must be able to point to specific, articulable facts relating to the person stopped that are indicative of involvement in a criminal offense. Department policies likewise mirror these admonitions. See, e.g., Seattle Police Department Manual § 6.220 (defining “reasonable suspicion” as requiring “specific, objective, articulable facts” that “would create a well-founded suspicion that there is a substantial possibility” of criminal conduct); NYPD Patrol Guide § 212-11 (“The officer must be able to articulate specific facts establishing justification for the stop; hunches or gut feelings are not sufficient.”). In Terry itself, the Court relied on the fact that Officer MacFadden had seen three men take turns walking by the same store 24 times and peering into the window, conferring with one another in between trips—behavior that MacFadden concluded was strongly indicative of an impending robbery. The Court recognized that, in these circumstances, although MacFadden lacked probable cause to make an arrest, it was reasonable for him to briefly detain Terry to confirm or dispel his suspicions. 392 U.S. at 4.

In the decades after Terry was decided, however, courts—including the U.S. Supreme Court—have interpreted reasonable suspicion to require much less than the constellation of facts that had prompted Officer MacFadden to act. In Illinois v. Wardlow, 120 S. Ct. 673 (2000), for example, the Court upheld a stop based on “unprovoked flight” from the police in a “high crime area.” As many have since pointed out, factors such as these may not be indicative of criminality, particularly in communities in which there is considerable fear or mistrust of the police. See, e.g., Commonwealth v. Warren, 58 N.E.3d 333, 342 (Mass. 2016) (the fact that in some communities Black and Hispanic males are disproportionately singled out by the police “suggests a reason for flight totally unrelated to consciousness of guilt.”). Courts also have permitted stops at airports and bus terminals based on a drug-courier profile that deems virtually all conduct potentially suspect. As Judge Pratt pointed out in U.S. v. Hooper, a traveler’s actions under the profile may be suspicious if the person “arrived late at night” or “arrived early in the morning”; used a “one-way ticket” or a “round-trip ticket”; “traveled alone” or “travelled with a companion”; “acted too nervous” or “acted too calm”—just to name a few. 935 F.2d 484, 499 (2d Cir. 1991) (Pratt, J., dissenting); see also United States v. Sokolow, 831 F.2d 1413, 1418 (9th Cir. 1987), rev’d 490 U.S. 1 (1989) (noting the profile’s “chameleon-like way of adapting to any particular set of observations”).

Officers in agencies across the country have relied on these sorts of nebulous factors to justify literally millions of stops, an overwhelming percentage of which have failed to turn up any evidence. In New York, for example, researchers found that a majority of the more than 4.4 million stops were justified based on factors such as the suspect being in a “high crime area” or exhibiting “furtive movements.” Jeffrey Fagan & Amanda Geller, Following the Script: Narratives of Suspicion in Terry Stops in Street Policing, 82 U. Chi. L. Rev. 51 (2015). Officers recovered guns in just 0.1 percent (one-tenth of one percent) of stops. See Floyd v. New York, 959 F. Supp. 2d 540, 542 (S.D.N.Y. 2013). Philadelphia police stopped more than 200,000 pedestrians in the first half of 2012, and recovered just three guns. See Barry Friedman & Cynthia Benin Stein, Redefining What’s “Reasonable”: The Protections for Policing, 84 Geo. Wash. L. Rev. 281 (2016) (citing these and other comparable statistics); Bernard E. Harcourt & Tracey L. Meares, Randomization and the Fourth Amendment, 78 U. Chi. L. Rev. 809, 854-858 (2011) (citing additional studies).

In addition to the sheer number of stops that produce no evidence of criminality, the evidence is overwhelming that when stops are used with frequency, the impact of those stops falls disproportionately—often extremely disproportionately—on people of color. In New York, Black and Hispanic individuals accounted for 52 percent of the population, and 83 percent of individuals stopped. Floyd, supra, at 559. In Los Angeles, one study found that African Americans were more than 2.5 times more likely to be stopped than were whites. Ian Ayres & Jonathan Borowsky, A Study of Racially Disparate Outcomes in the Los Angeles Police Department (2008). See also U.S. Dept. of Justice, Investigation of the Newark Police Department 19 (2014) (hereinafter Newark DOJ Report) (finding that stops disproportionately impacted minority residents); U.S. Dept. of Justice, Investigation of the Newark Police Department 47 (2016) (same).

A federal court ultimately found that the justification New York City Police Department (NYPD) officers provided for a substantial percentage of stops fell short of reasonable suspicion. But it is hard to deny that the permissive stance that courts generally have adopted in defining “reasonable suspicion” has given officers considerable leeway to conduct these sorts of encounters. Given the courts’ permissive stance, these Principles are designed to provide officers and agencies with more sturdy guidance to ensure that encounters are safe, productive, and supportive of more trusting relationships between officers and members of the public.

Although a few scholars have argued in favor of abandoning the reasonable-suspicion standard and replacing it with a more stringent probable-cause standard, these Principles advocate instead a return to the principles articulated in Terry itself. Throughout the opinion, the Justices emphasized the need for “specificity in the information upon which police action is predicated”—and detailed at length the constellation of facts that MacFadden had observed over a period of time that led him to suspect Terry and his companions of planning a robbery. In Terry, Officer MacFadden briefly stopped three individuals he suspected of committing a “particular crime[] in progress.” Today, agencies instruct officers to “proactively polic[e] people that they suspect could be offenders.” Tracey L. Meares, Programming Errors: Understanding the Constitutionality of Stop-and-Frisk as a Program, Not an Incident, 82 U. Chi. L. Rev. 1, 164 (2015).

Importantly, these Principles make clear that officers should be able to articulate not only the basis for their suspicion, but also the particular offense they that they suspect. See, e.g., Tucson Police Department General Order 2214.1 (adopting this standard); Friedman & Stein, supra at 347 (advocating this approach). This standard would help to ensure that officer suspicions are indeed based on more than a mere “hunch.” In addition, this standard would encourage officers to pay more attention to behavioral cues indicative of criminal activity (which, like “casing,” typically are indicative of a particular crime), as opposed to non-behavioral characteristics such as location or manner of dress. Studies suggest that stops based on more specific, behavioral factors are more likely to turn up evidence or contraband and lead to overall reductions in crime. For example, a study conducted by the New York State Attorney General’s office of NYPD stop data found that stops based on factors that clearly gave rise to reasonable suspicion were substantially more likely to result in an arrest than were stops based on vaguer criteria that arguably fell short of reasonable suspicion. See Civil Rights Bureau, Office of the Attorney General, The New York City Police Department’s “Stop & Frisk” Practices (1999); see also Sharad Goel, Justin M. Rao & Ravi Shroff, Precinct or Prejudice? Understanding Racial Disparities in New York City’s Stop-and-Frisk Policy, 10 Ann. Appl. Stat. 365 (2016); Fagan, Terry’s Original Sin, 2016 U. Chi. Legal F. 43. Studies also suggest that officers are more likely to rely on non-behavioral cues in deciding whether to stop racial minorities. Geoffrey P. Alpert, John M. MacDonald & Roger G. Dunham, Police Suspicion and Discretionary Decision Making During Citizen Stops, 43 Criminology 407 (2005). To the extent that stops based on non-behavioral cues also are less effective, this raises serious procedural-justice concerns.

At the same time—in view of the difficulty that courts have had in defining the precise requirements of reasonable suspicion—these Principles do not advocate in favor of the approach followed in New York state, which requires causal thresholds for all encounters that legally fall short of a stop. Under People v. De Bour, 352 N.E.2d 562 (N.Y. 1976), officers in New York must have “an objective, credible reason” to approach a person on the street, and must have “founded suspicion that criminality is afoot” in order to ask more prying questions. As Professor Debra Livingston notes, the New York courts’ approach “has not really worked” to accomplish the goal of “protect[ing] individuals from arbitrary or intimidating police conduct.” Debra Livingston, Police Patrol, Judicial Integrity, and the Limits of Judicial Control, 72 St. John’s L. Rev. 1353 (1998). A survey of New York cases makes clear that “cases with almost identical facts produce different results.” Id. at 1361 n.12 (quoting Barry Kamins, New York Search and Seizure 103 (1997)); see also Wayne R. LaFave, 4 Search & Seizure § 9.4(e) (5th ed.) (noting similar confusion); Mark A. Leslie, The Gradation of Fourth Amendment Doctrine in the Context of Street Detentions: People v. De Bour, 38 Ohio St. L.J. 409 (1977) (expressing concern that “police may be prompted by lower requirements of suspicion to act more freely upon their instincts.”). Instead, these Principles urge agencies to ensure that officers understand that initial encounters may be unwelcome or nonconsensual, and that officers should—consistent with § 4.03—limit the use of such encounters to circumstances in which they directly further important law-enforcement interests and minimize harm. Officers also should minimize the intrusiveness of all encounters by following the principles of procedural justice outlined in § 4.03(b).

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