Montero-Camargo (defendant) is a Mexican citizen who was arrested by Border Patrol agents near a Border Patrol checkpoint near El Centro, California. The agents had received a tip from a driver that two cars with Mexican plates had made U-turns upon seeing a sign that the checkpoint was reopened. The agents investigated and saw two cars pull onto the southbound lane from the shoulder. The agents testified that that area of highway is commonly used for illegal drop offs because it is not visible from the checkpoint. They also testified that there are no nearby exits or roads that the drivers could have missed. One agent pulled over the first car, while the other agent followed the second car and saw that the driver, Montero-Camargo, was Hispanic. He pulled the car over and searched it when the other agent returned, finding bags of marijuana and a pistol. Montero-Camargo moved to suppress the evidence obtained from the stop as illegal under the Fourth Amendment. The district court denied his motion and he appealed to the Court of Appeals for the Ninth Circuit.