Probable cause

A grand jury is a jury empowered by law to conduct legal proceedings, investigate potential criminal conduct, and determine whether criminal charges should be brought. A grand jury may subpoena physical evidence or a person to testify. A grand jury is separate from the courts, which do not preside over its functioning.

Originating in England during the Middle Ages, modern examples include grand juries in the United States, and to a lesser extent, Liberia. In Japan, there are citizen Prosecutorial Review Commissions which review cases that have been dropped by the prosecution, but they are not required for an indictment like in the previous two. Grand juries perform both accusatory and investigatory functions. The investigatory functions of grand juries include obtaining and reviewing documents and other evidence, and hearing sworn testimonies of witnesses who appear before it; the accusatory function determines whether there is probable cause to believe that one or more persons committed a particular offense within the jurisdiction of a court. While most grand juries focus on criminal matters, some civil grand juries serve an independent watchdog function. Around the 18th and 19th-century in Ireland and the U.S., grand juries were occasionally formed to pass or approve public policy.

The Fourth Amendment (Amendment IV) 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 (important or not).

Fourth Amendment case law deals with three main issues: what government activities are "searches" and "seizures", what constitutes probable cause to conduct searches and seizures, and how to address violations of Fourth Amendment rights. Early court decisions limited the amendment's scope to physical intrusion of property or persons, but with Katz v. United States (1967), the Supreme Court held that its protections extend to intrusions on the privacy of individuals as well as to physical locations. A warrant is needed for most search and seizure activities, but the Court has carved out a series of exceptions for consent searches, motor vehicle searches, evidence in plain view, exigent circumstances, border searches, and other situations.

Reasonable suspicion or reasonable articulable suspicion is a legal standard of proof that in United States law 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 (by feeling something that could be a weapon or contraband, for example), 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.

Beck v. Ohio, 379 U.S. 89 (1964), is a United States Supreme Court decision concerning evidence obtained by a search incidental to a good-faith warrantless arrest. Reversing the Ohio Supreme Court's decision, the U.S Supreme Court held that the record did not show facts sufficient for the Court to find that Ohio police arrested defendant with probable cause, so the criminally-punishable evidence found on his person during an incidental search was inadmissible. Accordingly, the Court vacated defendant's conviction.

The motor vehicle exception is a legal rule in the United States that modifies the normal probable cause requirement of the Fourth Amendment to the United States Constitution and, when applicable, allows a police officer to search a motor vehicle without a search warrant.

In United States criminal law, the border search exception is a doctrine that allows searches and seizures at international borders and their functional equivalent without a warrant or probable cause. Generally speaking, searches within 100 miles (160 km) of the border are more permissible without a warrant than those conducted elsewhere in the U.S. The doctrine also allows federal agents to search people at border crossings without a warrant or probable cause. The government is allowed to use scanning devices and to search personal electronics. Invasive bodily searches, however, require reasonable suspicion.

False arrest, unlawful arrest or wrongful arrest is a common law tort, where a plaintiff alleges they were held in custody without probable cause, or without an order issued by a court of competent jurisdiction. Although it is possible to sue law enforcement officials for false arrest, the usual defendants in such cases are private security firms.

Warrantless searches are searches and seizures conducted without court-issued search warrants.

In the United States, warrantless searches are restricted under the Fourth Amendment to the United States Constitution, part of the Bill of Rights, which states, "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."

In the law, the totality of the circumstances test refers to a method of analysis where decisions are based on all available information rather than bright-line rules. Under the totality of the circumstances test, courts focus "on all the circumstances of a particular case, rather than any one factor". In the United States, totality tests are used as a method of analysis in several different areas of the law. For example, in United States criminal law, a determination about reasonable suspicion or probable cause is based on a consideration of the totality of the circumstances.