United States v. Brignoni-Ponce

The government’s substantial interest in effectively deterring illegal aliens from entering this country outweighs the minimal intrusion of a brief stop and questioning of a vehicle and its occupants at the border. However, the Court held that stops made by “roving” patrols on a random basis were unreasonable under the Fourth Amendment. Only “when an officer’s observations lead him reasonably to suspect that a particular vehicle may contain aliens who are illegally in the country, may he stop the car briefly and investigate the circumstances that provoke suspicion.” Similarly, the Fourth Amendment prohibits detaining individuals for questioning about their citizenship unless reasonable suspicion exists that the individual is an illegal alien.

Here, the only basis for stopping the vehicle and questioning the occupants was the fact the occupants appeared to be of Mexican ancestry. Standing alone, this does not furnish reasonable suspicion to believe the occupants were illegal aliens. Facts that Border Patrol agents may rely upon to establish reasonable suspicion include (1) the location of the area where the vehicle was encountered, including its proximity to the border, the usual patterns of traffic on the road, and previous experience with alien traffic; (2) information about recent border crossings in the area; (3) the driver’s behavior, such as erratic driving or obvious attempts to evade officers; and (4) aspects of the vehicle itself, such as its size, the number of passengers, and whether it appears heavily loaded.