Русско-англо-русский юридический словарь

catch red-handed. Also, catch in the act. Apprehend someone in the course of wrongdoing, as in The boys were trying to steal a car and the police caught them red-handed, or He tried to cheat on the exam, but his teacher walked in and caught him in the act. The first term referred to blood on a murderer's hands and originally signified only that crime. Later it was extended to any offense. The variant ( catch in the act) is a translation of the Latin in flagrante delicto, part of the Roman code and long used in English law. (The American Heritage® Dictionary of Idioms by Christine Ammer)

A mass arrest occurs when police apprehend large numbers of suspects at once. This sometimes occurs at illegal protests. Some mass arrests are also used in an effort to combat gang activity. (Wikipedia)

The territorial principle (also territoriality principle) is a principle of public international law which enables a sovereign state to exercise exclusive jurisdiction over individuals and other legal persons within its territory. It includes both the right to prosecute individuals for criminal offenses committed within its borders, as well as the right to arrest and apprehend individuals within its territory. (Wikipedia)