in the United States, there is a history of limitation of occupying armies, and to some extent police. It comes from a time when you, citizen, had to stop what

in the United States, there is a history of limitation of occupying armies, and to some extent police. It comes from a time when you, citizen, had to stop what you are doing and become under questioning or controlled without any checks and balances. A group of men in uniform could stop and hold any number of people for "suspicion" .. that is illegal here. So in reverse, if you are going to be stopped, questioned, and your actions controlled, there must be sufficient reason, and that authority has limitations. Cars have changed that calculus a lot, laws are being updated. Murky legal waters for "searching" crowds.. one factor is that information systems hold data for days and years, millions of records can be searched instantly on a regular basis. so the practical reach of technology has changed. IANAL