What is the test for establishing reasonable suspicion for an investigatory stop?

We review de novo whether reasonable suspicion existed for an investigatory stop. United States v. Franco-Munoz, 952 F.2d 1055, 1056 (9th Cir.1991). Even though we review this mixed question of law and fact de novo, we review the establishment of underlying basic facts for clear error. United States v. McConney, 728 F.2d 1195, 1200-02 (9th Cir.) (en banc), cert. denied, 469 U.S. 824 (1984). Such review entails "due regard" for the district court's credibility determinations. Amadeo v. Zant, 486 U.S. 214, 223 (1988).

"[O]fficers on roving patrol may stop vehicles only if they are aware of specific articulable facts, together with rational inferences from those facts, that reasonably warrant suspicion...." United States v. Brignoni-Ponce, 422 U.S. 873, 884 (1975). Such a stop requires an "objective manifestation that the person stopped is, or is about to be, engaged in criminal activity." United States v. Cortez, 449 U.S. 411, 417 (1981). The totality of circumstances must present "a particularized and objective basis for suspecting the particular person stopped of criminal activity." Id. at 417-18. An officer assesses the circumstances based on probabilities, not certainties, and, based on his or her training, draws inferences that might elude the untrained person. Id. at 418.