Investigatory Stops of Persons. Not all encounters between individuals and police are seizures governed by the Fourth Amendment. A seizure occurs when a reasonable person (1) would not feel “free to leave” or (2) would not feel “free to decline the officers' requests or otherwise terminate the encounter.” Investigatory stops--brief seizures by police officers that fall short of traditional arrests--are governed by the Fourth Amendment and are lawful when justified by a reasonable suspicion that an individual is engaged in criminal activity. Reasonable suspicion, a lesser standard than probable cause, exists when an officer can “point to specific and articulable facts, which, taken together with rational inferences from those facts, reasonably warrant th[e] intrusion.” Inarticulable hunches or generalized suspicions are insufficient. In adopting this formulation, the Supreme Court in Terry v. Ohio emphasized the importance of balancing “the need to search (or seize) against the invasion which the search (or seizure) entails” to determine whether a search or seizure is lawful.
To determine whether reasonable suspicion existed at the time of the encounter, courts use a “totality of the circumstances” test. Police may stop and question a person for a limited period of time when they reasonably suspect that the person is engaged in criminal activity. The requirements for performing an investigatory frisk are discussed later in this Section.
Generally, investigatory stops are valid only if the suspicion is objectively reasonable. An officer's subjective intentions are irrelevant to the constitutionality of an investigatory stop under the Fourth Amendment. The primary bases for reasonable suspicion are a police officer's personal observations and the officer's knowledge obtained or imputed from others that a crime has been committed. Courts afford considerable deference to the observations and conclusions of the police, reasoning that an experienced officer can infer criminal activity from conduct that may seem innocuous to a lay observer.
Isolated or minimal instances of innocent activity are insufficient to constitute reasonable suspicion, but several apparently innocent activities taken together may meet the required standard.
Reliable information from an informant may also create reasonable suspicion and justify an investigatory stop. Courts assess the reliability of an informant's tip on a sliding scale: greater corroboration is necessary to justify acting on a tip from an unknown informant or an informant of uncertain trustworthiness, whereas less corroboration will suffice if the information is from a known source or a source that has proven trustworthy in the past.
The presence of a suspect in a high-crime neighborhood does not, standing alone, justify seizure. Courts may use these factors, however, in assessing the totality of circumstances surrounding a seizure. For example, a suspect's unprovoked flight upon seeing the police can justify a seizure when it occurs in a high-crime neighborhood. Generalized suspicion of criminal activity based solely on race does not justify a seizure.
Police activities during an investigatory stop must be reasonably related to the circumstances that initially justified the stop. During a lawful investigatory stop, police may ask questions or request documents to establish a person's identity and to confirm or dispel suspicions of criminal activity. If reasonable suspicion does not exist, police may still order occupants out of a vehicle they have lawfully stopped. In addition to detentions that are justified in the absence of a warrant, a detention may be justified because a valid search warrant to search for contraband founded on probable cause implicitly carries with it the limited authority to detain the occupants on or in immediate vicinity of the premises while the search is conducted.
When the police hold a suspect beyond the amount of time necessary to effectuate the purpose of the stop, the seizure becomes an arrest and must be supported by probable cause. The Supreme Court has declined to establish a bright-line rule to determine when an investigatory stop becomes an arrest. Instead, whether an investigatory stop has become an arrest is decided on a case-by-case basis. In making such decisions, courts consider the diligence of police in resolving their reasonable suspicion as quickly as possible, the scope and nature of the restraints placed on an individual's liberty, and whether police transported the individual to another location. The mere existence of a less intrusive means of investigation does not make a detention unreasonable. When a detainee's own actions contribute to the duration of a stop, a longer detention may be reasonable.
Under Terry, a police officer who makes an investigatory stop may conduct a limited pat-down, or frisk, of a suspect's outer clothing. The frisk may be conducted only if the officer has a reasonable belief that the detainee poses a threat to the officer's safety or the safety of others. Its scope must be limited to a search for weapons and may not be used to search for evidence of criminal activity.