Citizen's arrest

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 England 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 country in which they are acting. For example, in the British jurisdiction of England and Wales, the power comes from section 24A(2) of the 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.

A person who makes a citizen's arrest could risk exposing him or herself to possible lawsuits or criminal charges – such as charges of false imprisonment, unlawful restraint, kidnapping, or wrongful arrest – if the wrong person is apprehended or a suspect's civil rights are violated. This is especially true when police forces are attempting to determine who an aggressor is.

The level of responsibility that a person performing a citizen's arrest may bear depends on the jurisdiction. For instance, in France and Germany, a person stopping a criminal from committing a crime, including crimes against belongings, is not criminally responsible as long as the means employed are in proportion to the threat. Note, however, that in both countries, this results from a different legal norm, "aid to others in immediate danger," which is concerned with prevention, not prosecution, of crimes.

...
Wikipedia