The Fourth Amendment to the United States Constitution is part of the Bill of Rights. It prohibits unreasonable searches and seizures. In addition, it 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."
Search and seizure is a procedure used in many civil law and common law legal systems by which police or other authorities and their agents, who, suspecting that a crime has been committed, commence a search of a person's property and confiscate any relevant evidence found in connection to the crime.
In criminal procedure law of the United States, an exigent circumstance allows law enforcement to enter a structure without a search warrant, or if they have a "knock and announce" warrant, allows them to enter without knocking and waiting for the owner's permission to enter. It must be a situation where people are in imminent danger, evidence faces imminent destruction, or a suspect's escape is imminent. Once entry is obtained, the plain view doctrine applies, allowing the seizure of any evidence or contraband discovered in the course of actions consequent upon the exigent circumstances.
United States v. Ross, 456 U.S. 798 (1982), was a search and seizure case argued before the Supreme Court of the United States. The high court was asked to decide if a legal warrantless search of an automobile allows closed containers found in the vehicle to be searched as well. The appeals court had previously ruled that opening and searching the closed portable containers without a warrant was a violation of the Fourth Amendment, even though the warrantless vehicle search was permissible due to existing precedent.
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.
Atwater v. Lago Vista, 532 U.S. 318 (2001), was a United States Supreme Court decision which held that a person's Fourth Amendment rights are not violated when the subject is arrested for driving without a seatbelt. The court ruled that such an arrest for a misdemeanor that is punishable only by a fine does not constitute an unreasonable seizure under the Fourth Amendment.
Brigham City v. Stuart, 547 U.S. 398 (2006), is a United States Supreme Court case involving the exigent circumstances exception to the Fourth Amendment's warrant requirement. The Court ruled that police may enter a home without a warrant if they have an objectively reasonable basis for believing that an occupant is or is about to be seriously injured.
Ker v. California, 374 U.S. 23 (1963), was a case before the United States Supreme Court, which incorporated the Fourth Amendment's protections against illegal search and seizure. The case was decided on June 10, 1963, by a vote of 5–4.
Welsh v. Wisconsin, 466 U.S. 740 (1984), was a 1983 case before the US Supreme Court determining that a warrantless home arrest without exigent circumstances violates the Fourth Amendment protection against unlawful search and seizure.
Maryland v. Pringle, 540 U.S. 366 (2003), was a decision by the Supreme Court of the United States in which the Court unanimously upheld the arrest of three passengers in an automobile where drugs were found. The case regards the reasonableness of the arrest of a passenger in an automobile.
Carroll v. United States, 267 U.S. 132 (1925), was a decision by the United States Supreme Court that upheld the warrantless searches of an automobile, which is known as the automobile exception. The case has also been cited as widening the scope of search.
Arizona v. Gant, 556 U.S. 332 (2009), was a United States Supreme Court decision holding that the Fourth Amendment to the United States Constitution requires law-enforcement officers to demonstrate an actual and continuing threat to their safety posed by an arrestee, or a need to preserve evidence related to the crime of arrest from tampering by the arrestee, in order to justify a warrantless vehicular search incident to arrest conducted after the vehicle's recent occupants have been arrested and secured.
Almeida-Sanchez v. United States, 413 U.S. 266 (1973), was a United States Supreme Court case holding that the search of an automobile by the United States Border Patrol without a warrant or probable cause violates the Fourth Amendment. The vehicle was stopped and searched for illegal aliens twenty-five miles (40 km) from the Mexican border. The Court approached the search from four views: automobile search, administrative inspection, heavily regulated industry inspection, and border search. As to the validity of the search under the automobile exception, the Court found no justification for the search under the Carroll doctrine because there was no probable cause. As to the validity of the search under various administrative inspection doctrines, the Court found that the officers lacked an area warrant. As to the validity of the heavily regulated industry inspection, the Court found that the doctrine is not applicable to traveling on a state highway. As to the validity of a border search, the Court found that the site of the stop and the entirety of the road on which the stop occurred was too far from the border to be considered a border search.
Whren v. United States, 517 U.S. 806 (1996), was a unanimous United States Supreme Court decision that "declared that any traffic offense committed by a driver was a legitimate legal basis for a stop."
Ornelas v. United States, 517 U.S. 690 (1996), was a case decided by the Supreme Court of the United States that held that appellate courts should review probable cause determinations for warrantless searches de novo.
Kentucky v. King, 563 U.S. 452 (2011), was a decision by the US Supreme Court, which held that warrantless searches conducted in police-created exigent circumstances do not violate the Fourth Amendment as long as the police did not create the exigency by violating or threatening to violate the Fourth Amendment.
County of Riverside v. McLaughlin, 500 U.S. 44 (1991), was a United States Supreme Court case which involved the question of within what period of time must a suspect arrested without a warrant be brought into court to determine if there is probable cause for holding the suspect in custody. The majority held that suspects must generally be granted a probable cause determination within 48 hours of arrest. The dissent believed that probable cause hearings should generally be provided much sooner, as soon as the police complete the administrative steps incident to arrest.
United States v. Watson, 423 U.S. 411 (1976), was a case decided by the Supreme Court of the United States that decided that a warrantless arrest in public and consenting to a vehicle search did not violate the Fourth Amendment.
Johnson v. United States, 333 U.S. 10 (1948), was a significant United States Supreme Court decision addressing search warrants and the Fourth Amendment. In this case, where federal agents had probable cause to search a hotel room but did not obtain a warrant, the Court declared the search was "unreasonable."
