Reasonable suspicion To possess reasonable suspicion that would justify a stop, police must have "specific and articulable facts" that indicate that the person to be stopped is, or is about to be, engaged in criminal activity. Because officers usually do not have supervision when they encounter civilians, they have discretion regarding whom to stop. Reasonable suspicion depends on the "
totality of the circumstances". Reasonable suspicion is a vague term, and the Supreme Court concluded that it is to be decided on a case-by-case basis. It often arises from a combination of facts, each of which would, in itself, not be enough justification for the stop. The suspicion must be that of an individual person. Police officers primarily use situational factors based on criminal behavior to determine whether a stop is needed. In essence, when they witness a person behaving suspiciously or violating the law, they are constitutionally permitted to stop them. Other factors informing the decision include personal attitudes and the decision-making model in effect where the officer works. These subjective influences naturally create the opportunity for bias on the part of police officers who possess animus toward a certain class of people. For instance, a social interaction such as a hug or a handshake might be perceived as a drug deal. Before 1968, the law required substantial evidence to impede liberty or seize property. However, the Fourth Amendment does not protect consensual encounters. In its
Terry decision, the
Supreme Court found that the police should have the power to search, even without probable cause, to protect themselves from weapons. The cases following
Terry expanded the power of the police. While the original case was concerned with armed violence and firsthand observation by officers,
Adams v. Williams (1972) extended the doctrine to
drug possession substantiated by the secondhand hearsay of an informant. The
Adams v. Williams case set a precedent that police are not required to directly observe suspicious behavior if their reasonable suspicion is based upon information provided by a confidential informant. In
Illinois v. Wardlow (2000), a person's unprovoked flight from
Chicago police officers in "an area known for heavy narcotics trafficking" constituted reasonable suspicion to stop him. During
Terry stops, police usually ask detainees to identify themselves. Several states require people to provide their names to the police upon request. In
Hiibel v. Sixth Judicial District Court of Nevada (2004), these
stop-and-identify statutes were deemed constitutional. While the specifics of stop-and-identify statutes and ordinances vary, a significant number of states and local jurisdictions have enacted such laws. In
New York, courts have limited the effects of
Terry by creating a four-level continuum of intrusion, each of which requires its own level of suspicion. This allows police officers to detain people if the officers possess an articulable and objectively credible reason. In
People v. DeBour, New York's highest court permitted the police to stop a person who simply crosses the street upon observing the police. Lacking reasonable suspicion, police may stop a person based on a hunch, constituting a
consensual stop.
United States v. Mendenhall found that police are not generally required to advise an individual that the stop is on a consensual basis nor that the person may leave at any time. A person can typically determine whether a stop is consensual by asking, "Am I free to go?". If the officer responds in the negative or does not respond, the person is being detained under a
Terry stop; otherwise, the person may leave.
Mendenhall also found that a consensual stop can be converted into an unconstitutional
Terry stop by circumstances such as "the threatening presence of several officers, the display of a weapon by an officer, some physical touching of the person of the citizen, or the use of language or tone of voice indicating that compliance with the officer's request might be compelled." Police who conduct an unconstitutional
Terry stop can face administrative discipline and civil suits. In
Pennsylvania v. Mimms, two police officers issued Mimms a ticket for driving a car with an expired license plate. When they asked him to step out, they realized that he had a gun, and promptly arrested him. The court ruled in favor of the police, citing officer safety as their reason. Dissenting justices found that this furthers the expansion of
Terry. They feared that the ruling set a precedent that officers could ask citizens to perform actions through warrantless intrusion. However, pursuant to the plain-feel doctrine (similar to the
plain-view doctrine), police may seize
contraband discovered in the course of a frisk, but only if the type of contraband is immediately apparent. Subsequent court cases have expanded the definition of what constitutes a frisk and what is considered as
admissible evidence. In
Michigan v. Long,
Terry stops were extended to searching the inside of a car passenger compartment if police have reasonable suspicion that an occupant may have access to a weapon there. In
Minnesota v. Dickerson, the court ruled that "immediately recognized" contraband discovered during a
Terry stop is also a lawful seizure. ====
Consensual search ==== Based on the Supreme Court decision in
Schneckloth v. Bustamonte (1972), a person waives Fourth Amendment protections when voluntarily
consenting to a search. Police are not required to inform a person of their right to decline the search. Justice Marshall, in his dissent, wrote that it is a "curious result that one can choose to relinquish a constitutional right—the right to be free from unreasonable searches—without knowing that he has the alternative of refusing to accede to a police request." Several cities and states require police to inform citizens of their right to deny a search. == Traffic stops ==