The Border Patrol operates a fixed checkpoint on Interstate Highway 5 south of San Clemente. The checkpoint was closed because of the weather, but two officers were observing northbound traffic from a patrol car parked at the side of the highway. The road was dark, and they were using the patrol car's headlights to illuminate passing cars. They stopped D's car. Their only reason was that its three occupants appeared to be of Mexican descent. The officers questioned D and his two passengers about their citizenship and learned that the passengers were aliens who had entered the country illegally. All three were then arrested, and D was charged with two counts of knowingly transporting illegal immigrants, a violation of § 274 (a) (2) of the Immigration and Nationality Act. D moved to suppress the testimony claiming the evidence was the fruit of an illegal seizure. The trial court denied the motion. The aliens testified at trial, and D was convicted on both counts. The Court of Appeals held that the stop, in this case, more closely resembled a roving-patrol stop than a stop at a traffic checkpoint. Under Almeida-Sanchez v. United States, the Fourth Amendment prohibits the use of roving patrols to search vehicles, without a warrant or probable cause, at points removed from the border and its functional equivalents. It held that unless the officers have a 'founded suspicion' that the occupants are aliens illegally in the country their mere Mexican ancestry alone did not support such a 'founded suspicion.' P appealed.