Posse comitatus

An American posse in 1922, which captured the outlaws Manuel Martinez and Placidio Silvas, who are in the center of the back row. Martinez and Silvas were arrested for the Ruby Murders after the largest manhunt in the history of the Southwest.

The posse comitatus (/ˌpɒsi ˌkɒmɪˈteɪtəs, -ˈtɑːtəs/; from Latin for "force of the county" or "ability to have a retinue or gang"), frequently shortened to posse, is in common law a group of people mobilized to suppress lawlessness, defend the people, or otherwise protect the peace, property, and public welfare. It may be called by the conservator of peace – typically a reeve, sheriff, chief, or another special/regional designee like an officer of the peace potentially accompanied by or with the direction of a justice or ajudged parajudicial process given the imminence of actual damage. There must be a lawful reason for a posse, which can never be used for lawlessness. The posse comitatus as a doctrine defined in English jurisprudence dates back to 9th-century England.