The Fourth Amendment to the United States Constitution is part of the Bill of Rights. It prohibits unreasonable searches and seizures and sets requirements for issuing warrants: warrants must be issued by a judge or magistrate, justified by probable cause, supported by oath or affirmation, and must particularly describe the place to be searched and the persons or things to be seized.
In United States criminal law, probable cause is the standard by which police authorities have reason to obtain a warrant for the arrest of a suspected criminal or the issuing of a search warrant. There is no universally accepted definition or formulation for probable cause. One traditional definition, which comes from the U.S. Supreme Court's 1964 decision Beck v. Ohio, is when "whether at [the moment of arrest] the facts and circumstances within [an officer's] knowledge and of which they had reasonably trustworthy information [are] sufficient to warrant a prudent [person] in believing that [a suspect] had committed or was committing an offense."
Terry v. Ohio, 392 U.S. 1 (1968), was a landmark U.S. Supreme Court decision in which the court ruled that it is constitutional for American police to "stop and frisk" a person they reasonably suspect to be armed and involved in a crime. Specifically, the decision held that a police officer does not violate the Fourth Amendment to the U.S. Constitution's prohibition on unreasonable searches and seizures when questioning someone even though the officer lacks probable cause to arrest the person, so long as the police officer has a reasonable suspicion that the person has committed, is committing, or is about to commit a crime. The court also ruled that the police officer may perform a quick surface search of the person's outer clothing for weapons if they have reasonable suspicion that the person stopped is "armed and presently dangerous." This reasonable suspicion must be based on "specific and articulable facts," and not merely upon an officer's hunch.
A Terry stop in the United States allows the police to briefly detain a person based on reasonable suspicion of involvement in criminal activity. Reasonable suspicion is a lower standard than probable cause which is needed for arrest. When police stop and search a pedestrian, this is commonly known as a stop and frisk. When police stop an automobile, this is known as a traffic stop. If the police stop a motor vehicle on minor infringements in order to investigate other suspected criminal activity, this is known as a pretextual stop. Additional rules apply to stops that occur on a bus.
Reasonable suspicion is a legal standard of proof in United States law that is less than probable cause, the legal standard for arrests and warrants, but more than an "inchoate and unparticularized suspicion or 'hunch'"; it must be based on "specific and articulable facts", "taken together with rational inferences from those facts", and the suspicion must be associated with the specific individual. If police additionally have reasonable suspicion that a person so detained is armed and dangerous, they may "frisk" the person for weapons, but not for contraband like drugs. However, if the police develop probable cause during a weapons frisk, they may then conduct a full search. Reasonable suspicion is evaluated using the "reasonable person" or "reasonable officer" standard, in which said person in the same circumstances could reasonably suspect a person has been, is, or is about to be engaged in criminal activity; it depends upon the totality of circumstances, and can result from a combination of particular facts, even if each is individually innocuous.
"Stop and identify" statutes are laws in several U.S. states that authorize police to lawfully order people whom they reasonably suspect of committing a crime to state their name. If there is not reasonable suspicion that a person has committed a crime, is committing a crime, or is about to commit a crime, the person is not required to identify himself or herself, even in these states.
In the United States, open carry refers to the practice of visibly carrying a firearm in public places, as distinguished from concealed carry, where firearms cannot be seen by the casual observer. To "carry" in this context indicates that the firearm is kept readily accessible on the person, within a holster or attached to a sling. Carrying a firearm directly in the hands, particularly in a firing position or combat stance, is known as "brandishing" and may constitute a serious crime, but is not the mode of "carrying" discussed in this article.
Illinois v. Caballes, 543 U.S. 405 (2005), is a decision by the Supreme Court of the United States in which the Court held that the use of a drug-sniffing police dog during a routine traffic stop does not violate the Fourth Amendment to the U.S. Constitution, even if the initial infraction is unrelated to drug offenses.
Florida v. J. L., 529 U.S. 266 (2000), was a United States Supreme Court case in which the Court determined that a police officer may not legally stop and frisk someone based solely on an anonymous tip that describes a person's location and appearance, but does not furnish information as to any illegal conduct.
Frisking is a search of a person's outer clothing wherein a person runs their hands along the outer garments of another to detect any concealed weapons or objects.
Kolender v. Lawson, 461 U.S. 352 (1983), is a United States Supreme Court case concerning the constitutionality of vague laws that allow police to demand that "loiterers" and "wanderers" provide "credible and reliable" identification.
Commonwealth v. Matos, 672 A.2d 769 (1996), is a Pennsylvania State Supreme Court case which further developed Pennsylvania Constitutional Law as affording greater privacy protections than those guaranteed by the Fourth Amendment to the United States Constitution. Specifically, where police possess neither probable cause nor reasonable suspicion, contraband discarded by a person fleeing a police officer are the fruits of an illegal seizure. The case departs from the ruling of California v. Hodari D., 499 U.S. 621 (1991), which held that fleeing suspects cannot be considered seized for purposes of the U.S. Constitution. It is a part of a family of state case law concerning the phenomenon of "new judicial federalism." Pennsylvania criminal defense attorneys may cite the case as part of a motion to suppress physical evidence where the defendant discards drugs, weapons, or other contraband while fleeing police.
Pennsylvania v. Mimms, 434 U.S. 106 (1977), is a United States Supreme Court criminal law decision holding that a police officer ordering a person out of a car following a traffic stop and conducting a pat-down to check for weapons did not violate the Fourth Amendment to the United States Constitution.
United States v. Mendenhall, 446 U.S. 544 (1980), was a United States Supreme Court case that determined "seizure" occurs when an officer uses displays of authority to detain a person.
The stop-question-and-frisk program, or stop-and-frisk, in New York City, is a New York City Police Department (NYPD) practice of temporarily detaining, questioning, and at times searching civilians and suspects on the street for weapons and other contraband. This is what is known in other places in the United States as the Terry stop. The rules for the policy are contained in the state's criminal procedure law section 140.50 and based on the decision of the US Supreme Court in the case of Terry v. Ohio.
Heien v. North Carolina, 574 U.S. 54 (2014), was a decision by the United States Supreme Court, ruling that a police officer's reasonable mistake of law can provide the individualized suspicion required by the Fourth Amendment to the United States Constitution to justify a traffic stop. The Court delivered its ruling on December 15, 2014.
Rodriguez v. United States, 575 U.S. 348 (2015), was a United States Supreme Court case which analyzed whether police officers may extend the length of a traffic stop to conduct a search with a trained detection dog. In a 6–3 opinion, the Court held that officers may not extend the length of a traffic stop to conduct a dog sniff unrelated to the original purpose of the stop. However, the Court remanded the case to the United States Court of Appeals for the Eighth Circuit to determine whether the officer's extension of the traffic stop was independently justified by reasonable suspicion. Some analysts have suggested that the Court's decision to limit police authority was influenced by ongoing protests in Ferguson, Missouri.
Navarette v. California, 572 U.S. 393 (2014), was a case in which the United States Supreme Court clarified when police officers may make arrests or conduct temporary detentions based on information provided by anonymous tips. In 2008, police in California received a 911 call that a pickup truck was driving recklessly along a rural highway. Officers spotted a truck matching the description provided in the 911 call and followed the truck for five minutes, but did not observe any suspicious behavior. Nevertheless, officers conducted a traffic stop and discovered 30 pounds (14 kg) of marijuana in the truck. At trial, the occupants of the car argued that the traffic stop violated the Fourth Amendment of the United States Constitution, because the tip was unreliable, and officers did not personally observe criminal activity. Writing for a majority of the Court, Justice Clarence Thomas held that the 911 call was reliable, and that officers need not personally observe criminal activity when acting upon information provided by an anonymous 911 call.
United States v. Sharpe, 470 U.S. 675 (1985), was a legal case in which the Supreme Court of the United States clarified how long police are permitted to stop vehicles as part of an investigatory stop before it violates the Fourth Amendment to the U.S. Constitution.
