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.
A search warrant is a court order that a magistrate or judge issues to authorize law enforcement officers to conduct a search of a person, location, or vehicle for evidence of a crime and to confiscate any evidence they find. In most countries, a search warrant cannot be issued in aid of civil process.
In United States criminal law, probable cause is the legal standard by which police authorities have reason to obtain a warrant for the arrest of a suspected criminal and for a court's issuing of a search warrant. One definition of the standard derives from the U.S. Supreme Court decision in the case of Beck v. Ohio (1964), that probable cause exists when “at [the moment of arrest] the facts and circumstances within [the] knowledge [of the police], 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.”
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.
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.
In United States law, the Aguilar–Spinelli test was a judicial guideline set down by the U.S. Supreme Court for evaluating the validity of a search warrant or a warrantless arrest based on information provided by a confidential informant or an anonymous tip. The Supreme Court abandoned the Aguilar–Spinelli test in Illinois v. Gates, 462 U.S. 213 (1983), in favor of a rule that evaluates the reliability of the information under the "totality of the circumstances." However, Alaska, Hawaii, Massachusetts, New York, Vermont, Oregon, and Washington have retained the Aguilar–Spinelli test, based on their own state constitutions.
In common law, the fleeing felon rule permits the use of force, including deadly force, against an individual who is suspected of a felony and is in clear flight.
Tennessee v. Garner, 471 U.S. 1 (1985), is a civil case in which the Supreme Court of the United States held that, under the Fourth Amendment, when a law enforcement officer is pursuing a fleeing suspect, the officer may not use deadly force to prevent escape unless "the officer has probable cause to believe that the suspect poses a significant threat of death or serious physical injury to the officer or others."
An information is a formal criminal charge which begins a criminal proceeding in the courts. The information is one of the oldest common law pleadings, and is nearly as old as the better-known indictment, with which it has always coexisted.
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.
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.
Wilson v. Arkansas, 514 U.S. 927 (1995), is a United States Supreme Court decision in which the Court held that the traditional, common-law-derived "knock and announce" rule for executing search warrants must be incorporated into the "reasonableness" analysis of whether the actual execution of the warrant is/was justified under the 4th Amendment. The high court thus ruled that the old "knock and announce" rule while not a hard requirement, was also not a dead letter.
Rothgery v. Gillespie County, 554 U.S. 191 (2008), is a United States Supreme Court case in which the Court held that a criminal defendant's initial appearance before a magistrate judge, where he learns the charge against him and his liberty is subject to restriction, marks the initiation of adversary judicial proceedings that trigger attachment of the Sixth Amendment right to counsel. Attachment does not also require that a prosecutor be aware of that initial proceeding or involved in its conduct.
Florida v. Thomas, 532 U.S. 774 (2001), is a United States Supreme Court case decided in 2001. The case brought to the court concerned the extent of the Court's earlier decision in New York v. Belton, concerning whether a person was in custody, a determination central to allowing evidence seized in an automobile search to be presented in trial. However, the Court unanimously dismissed the case because the decision of the Florida state courts was not "final".
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.
Bailey v. United States, 568 U.S. 186 (2013), was a United States Supreme Court case concerning search and seizure. A 6–3 decision reversed the weapons conviction of a Long Island man who had been detained when police followed his vehicle after he left his apartment just before it was to be searched. Justice Anthony Kennedy wrote the majority opinion, and Antonin Scalia filed a concurrence. Stephen Breyer dissented.
Steagald v. United States, 451 U.S. 204 (1981), is a United States Supreme Court case which held that, based on the Fourth Amendment, a police officer may not conduct a warrantless search of a third party's home in an attempt to apprehend the subject of an arrest warrant, absent consent or exigent circumstances.
Maryland v. King, 569 U.S. 435 (2013), was a decision of the United States Supreme Court which held that a cheek swab of an arrestee's DNA is comparable to fingerprinting and therefore, a legal police booking procedure that is reasonable under the Fourth Amendment.
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.
Lange v. California, 594 U.S. ___ (2021), was a United States Supreme Court case involving the exigent circumstances requirement related to the Fourth Amendment to the United States Constitution. The Court ruled unanimously that the warrantless entry into a home by police in pursuit of a misdemeanant is not unequivocally justified.
