Detective Michael Pautz, a 20-year veteran of the Milwaukee County Sheriff's Department with 2 years specializing in drug enforcement, was conducting drug-interdiction surveillance in downtown Milwaukee. Pautz noticed a 1981 two-door Oldsmobile with California license plates in a motel parking lot. The car attracted Pautz's attention for two reasons: because older model, two-door General Motors cars are a favorite with drug couriers because it is easy to hide things in them; and because California is a 'source State' for drugs. Detective Pautz radioed his dispatcher to inquire about the car's registration. The dispatcher informed Pautz that the owner was either Miguel Ledesma Ornelas or Miguel Ornelas Ledesma from San Jose, California; Pautz was unsure which name the dispatcher gave. Detective Pautz checked the motel registry and learned that an Ismael Ornelas accompanied by a second man had registered at 4:00 a.m., without reservations. Pautz called for his partner, Donald Hurrle, a detective with approximately 25 years of law enforcement experience, assigned for the past 6 years to the drug enforcement unit. When Hurrle arrived at the scene, the officers contacted the local office of the Drug Enforcement Administration (DEA) and asked DEA personnel to run the names Miguel Ledesma Ornelas and Ismael Ornelas through NADDIS, a federal database of known and suspected drug traffickers. Both names appeared in NADDIS. The NADDIS report identified Miguel Ledesma Ornelas as a heroin dealer from El Centro, California, and Ismael Ornelas, Jr. as a cocaine dealer from Tucson, Arizona. The officers then summoned Deputy Luedke and the department's drug-sniffing dog, Merlin. Upon their arrival, Detective Pautz left for another assignment. Detective Hurrle informed Luedke of what they knew, and together they waited. Saul and Ismael Ornelas (D) emerged from the motel and got into the Oldsmobile. Detective Hurrle approached the car, identified himself as a police officer, and inquired whether they had any illegal drugs or contraband. Petitioners answered 'No.' Hurrle then asked for identification and was given two California driver's licenses bearing the names Saul Ornelas and Ismael Ornelas. Hurrle asked them if he could search the car and petitioners consented. The men appeared calm, but Ismael was shaking somewhat. Deputy Luedke, who over the past nine years had searched approximately 2,000 cars for narcotics, searched the Oldsmobile's interior. He noticed that a panel above the right rear passenger armrest felt somewhat loose and suspected that the panel might have been removed and contraband hidden inside. Luedke would testify later that a screw in the door jamb adjacent to the loose panel was rusty, which to him meant that the screw had been removed at some time. Luedke dismantled the panel and discovered two kilograms of cocaine. Ds were arrested. Ds filed pretrial motions to suppress, alleging that the police officers violated their Fourth Amendment rights when the officers detained them in the parking lot and when Deputy Luedke searched inside the panel without a warrant. The Government conceded in the court below that when the officers approached petitioners in the parking lot, a reasonable person would not have felt free to leave, so the encounter was an investigatory stop. An investigatory stop is permissible under the Fourth Amendment if supported by reasonable suspicion, Terry v. Ohio, 392 U.S. 1 (1968), and a warrantless search of a car is valid if based on probable cause, California v. Acevedo, 500 U.S. 565, 569 -570 (1991). The Magistrate Judge concluded that the circumstances gave the officers reasonable suspicion, but not probable cause. The Magistrate found, as a finding of fact, that there was no rust on the screw and hence concluded that Deputy Luedke had an insufficient basis to conclude that drugs would be found within the panel. The Magistrate nonetheless recommended that the District Court deny the suppression motions because he thought, given the presence of the drug-sniffing dog, that the officers would have found the cocaine by lawful means eventually and therefore the drugs were admissible under the inevitable discovery doctrine. Nix v. Williams, 467 U.S. 431 (1984). The District Court adopted the Magistrate's recommendation with respect to reasonable suspicion, but not its reasoning as to probable cause. The District Court thought that the model, age, and source-State origin of the car, and the fact that two men traveling together checked into a motel at 4 o'clock in the morning without reservations, formed a drug-courier profile and that this profile together with the NADDIS reports gave rise to reasonable suspicion of drug-trafficking activity; in the court's view, reasonable suspicion became probable cause when Deputy Luedke found the loose panel. Accordingly, the court ruled that the cocaine need not be excluded. Ds each plead guilty to possession of cocaine with intent to distribute. They reserved their right to appeal the District Court's denial of their motion to suppress the cocaine found in their car. The Court of Appeals reviewed deferentially the District Court's determinations of reasonable suspicion and probable cause; it would reverse only upon a finding of 'clear error.' The court found no clear error in the reasonable-suspicion analysis and affirmed that determination. With respect to the probable-cause finding, however, the court remanded the case for a determination on whether Luedke was credible when testifying about the loose panel. The District Court once again ruled that probable cause supported the search. The Seventh Circuit held that determination not clearly erroneous. The Supreme Court granted certiorari.