§ 3.01. Definition and Legality of Suspicion-Based Searches, Seizures, and Information Gathering

(a) For purposes of this Chapter, policing activity includes information gathering, seizures, and encounters, as those terms are used in Chapters 2, 3, and 4 of these Principles.

(b) As stated in § 2.01(a), a policing activity is “suspicion-based” when it is conducted with any cause to believe that the particular individual, place, or item subject to agency action is involved in prohibited conduct or is a threat to public safety, or that an individual is in need of aid.

(c) In addition to any other limitations imposed by the U.S. Constitution, suspicion-based policing activities should occur only if they are conducted pursuant to the Sections in this Chapter and, to the extent applicable, the more specific Sections governing encounters in Chapter 4.


a. Regulating suspicion-based policing activities. The Principles in this Chapter, and in Chapter 4 on encounters, provide a framework for regulating investigative activities that are targeted at a particular individual, place, or item based on any cause to believe that the subject is involved in unlawful conduct, is a threat to public safety, or is in need of aid. See § 2.01 (describing the distinction between suspicion-based and suspicionless policing activities). A policing activity is “suspicion-based” for the purposes of this Chapter even if it is based on little more than a hunch. What matters is that a government official has singled out a particular target for further scrutiny based on some belief that further investigation is warranted.

Suspicion-based policing poses a set of concerns that are different from those that arise when the government engages in suspicionless activities. See Chapter 5. For suspicion-based activities, a leading concern is that the individual, location, or item not be singled out inappropriately—either without sufficient justification or based on impermissible criteria. The protections discussed throughout Chapters 3 and 4 are designed to ensure that all targeted law-enforcement activity is conducted in a manner that minimizes unnecessary or arbitrary intrusions and, in doing so, preserves legitimacy and avoids undue harm.

As discussed in greater detail in § 2.01, Comment a, the line between suspicion-based and suspicionless activities can at times be murky, particularly when the government seeks to obtain information about all individuals who have some connection to a specific location where a crime has or is expected to occur. For these types of edge cases, the protections in Chapters 3 and 5 turn out to be quite similar, which obviates the need to place them firmly on either side of the line.

Reporters’ notes

Policing is “suspicion-based” whenever a government official singles out a particular individual, location, or item for further scrutiny. An officer who stops a person on the street based on a mere hunch that the individual is involved in criminal activity may lack the constitutionally requisite quantum of “suspicion” to justify the encounter. But that encounter nevertheless is suspicion-based for the purposes of these Principles.

This distinction mirrors the distinction the U.S. Supreme Court first articulated in Delaware v. Prouse, which made clear that “checkpoint-style” stops could be conducted in the absence of individualized suspicion, but that “roving” stops of specific vehicles could not. 440 U.S. 648 (1979); see also United States v. Brignoni-Ponce, 422 U.S. 873 (1975) (prohibiting roving immigration stops near the border in the absence of reasonable suspicion); United States v. Martinez-Fuerte, 428 U.S. 543 (1976) (permitting suspicionless checkpoint-style immigration stops). The Court explained that roving stops invite precisely “the kind of standardless and unconstrained discretion” that has animated the Court’s Fourth Amendment jurisprudence. Prouse, 440 U.S. at 661. Absent reasonable suspicion or probable cause to believe that the driver is violating a traffic regulation or is driving without a license, “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.” Id. What matters, in short, is whether an officer is targeting a specific person or implementing a general program aimed broadly at the general public or a clearly defined group. See also Camara v. Mun. Ct. of San Francisco, 387 U.S. 523, 532 (1967) (denouncing municipal inspections system whose “practical effect” was to “leave the occupant subject to the discretion of the official in the field,” but allowing searches that were in compliance with reasonable administrative scheme); Almeida-Sanchez v. United States, 413 U.S. 266, 270 (1973) (emphasizing the need to curb “unfettered discretion of members of the Border Patrol” to target individual vehicles).

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