What is sufficient to create a reasonable suspicion that criminal activity may be underway?

The police agents observed the two cars driving very closely together in tandem on a route near the border often used for smuggling. The occupants in the first car "stiffened" and both drivers "stared ahead" when the police car's headlights flashed upon them. The vehicles sped up when the police car began to follow them, and made a sudden turn in tandem onto a private dirt road without signaling. We agree with the district court that these circumstances were sufficient to create "a reasonable suspicion supported by articulable facts that criminal activity 'may be afoot.' " United States v. Sokolow, 109 S.Ct. 581, 585 (1989).

This result is consistent with our decision in United States v. Robert L., 874 F.2d 701 (9th Cir.1989), in which we recognized that the manner in which a suspect looks at or avoids eye contact with an officer, the manner in which he drives, and whether he is driving in tandem with another car, are relevant to a determination of founded suspicion. We held, however, that these factors did not support such a determination in the circumstances of that case. We concluded that the fact that the suspect "glanced quickly" at the agent "and then returned his eyes to the road" was normal because the agent was directing traffic at the scene of an accident; the fact that the suspect shifted lanes was "perfectly reasonable given that a marked patrol car was approaching in the lane behind him at 90 miles per hour;" and the officer's conclusion that the suspect was traveling "in tandem" with another automobile was "undercut" because it was based "only on the briefest of observations."