Probable cause are the facts and circumstances that would lead a person to believe that a person has committed a crime
A citizen's arrest is an arrest made by a person who is not acting as a sworn law-enforcement official. In common law jurisdictions, the practice dates back to medieval Britain and the English common law, in which sheriffs encouraged ordinary citizens to help apprehend law breakers.
Despite the practice's name, in most countries, the arresting person is usually designated as a person with arrest powers, who need not be a citizen of the jurisdiction or country in which he or she is acting. For example, in England/Wales, the power comes from Section 24 (4) (a) Police and Criminal Evidence Act 1984, called "any person arrest". This legislation states "any person" has these powers, and does not state that they need to be a British citizen.
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". 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. Reasonable suspicion is evaluated using the "reasonable person" or "reasonable officer" standard, in which said person in the same circumstances could reasonably believe 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.
In Terry v. Ohio, the U.S. Supreme Court ruled that a person can be stopped and briefly detained by a police officer based on a reasonable suspicion of involvement in a punishable crime. If the officer has reasonable suspicion that the person is armed and/or dangerous, the officer may perform a search of the person's outer garments for weapons. Such a detention does not violate the Fourth Amendment prohibition on unreasonable searches and seizure, though it must be brief. Reasonable suspicion does not provide grounds for arrest; however, an arrest can be made if facts discovered during the detention provide probable cause that the suspect has committed a crime.
Criminal law is the body of law that relates to crime. It regulates social conduct and proscribes threatening, harming, or otherwise endangering the health, safety, and moral welfare of people. It includes the punishment of people who violate these laws. Criminal law differs from civil law, whose emphasis is more on dispute resolution and victim compensation than on punishment.
In United States criminal law, probable cause (also referred to as reasonable cause) is the standard by which an officer or agent of the law has the grounds to obtain a warrant for, or as an exception to the warrant requirements for, making an arrest or conducting a personal or property search, etc. when criminal charges are being considered. It is also used to refer to the standard to which a grand jury believes that a crime has been committed. This term comes from the Fourth Amendment of the United States Constitution:
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.