We are asked in this appeal to determine whether, during an encounter between police officers and the appellant, Kelly Cor-dell, Cordell was illegally detained in violation of his right under the Fourth Amendment to be free from unreasonable seizures. We are also asked to determine whether the *1284government presented sufficient evidence at trial to show that Cordell knowingly possessed the cocaine with which he was found. Because we have determined that Cordell’s rights under the Fourth Amendment were not violated, and that the evidence against him was sufficient, we affirm Cordell’s conviction.
I.
Cordell was charged in a one count indictment with possession of cocaine with intent to distribute, 21 U.S.C. § 841(a)(1). He moved to suppress the cocaine, contending that it had been illegally seized. The district court held a suppression hearing and made findings of fact, which we summarize below.
On July 6, 1982, Chicago police officers Terrence O’Connor and Ricardo Abreu were assigned to narcotics duty at O’Hare International Airport. The officers were monitoring a non-stop flight to Chicago originating in Miami, a known “source” city for narcotics. The officers observed Cordell disembark from the Miami flight, carrying a travel bag. Cordell proceeded at a very rapid pace through the airport terminal. The officers followed Cordell at a distance as he proceeded down two escalators and into an open area that connects the terminals to the parking garage and the Hilton Hotel. The area is a well lighted public place. The officers approached Cordell from behind, and O’Connor said, “Pardon me, sir.” The officers identified themselves as police, and asked if Cordell would speak to them. Cordell agreed, and placed his travel bag on the floor beside him. O’Con-nor requested some identification, and Cor-dell produced his Wisconsin driver’s license. O’Connor then asked to see Cordell’s airline ticket. Cordell produced a ticket, purchased for cash, in the name of P. Baldwin. Cordell appeared extremely nervous during the conversation, but was polite and cooperative. O’Connor handed the ticket and license to Abreu, told Cordell they were conducting a narcotics investigation, and asked Cordell if he was carrying narcotics. When Cordell replied that he was not, O’Connor asked if Cordell would object to the officers looking in his travel bag. Cor-dell replied, “No, sir, go ahead.” O’Connor opened the bag and saw miscellaneous items of clothing and a large padded packing-type envelope. The envelope was sealed, addressed to a Milwaukee address with a Florida return address, and bore uncancelled stamps. O’Connor asked Cor-dell what was inside the envelope. Cordell replied that he did not know, as a man in the Miami airport had given it to him and asked him to deliver it to Milwaukee. O’Connor asked if Cordell would object if he opened the envelope. Cordell stated that he did not mind because the envelope was not his. O’Connor opened the envelope and observed a plastic bag containing a white powder. O’Connor then informed Cordell that he was under arrest, advised him of his rights, and escorted him to the Drug Enforcement Administration Office in the airport. The white powder discovered in Cordell’s bag was subsequently disclosed to be approximately 240 grams of fifty-percent cocaine.
The trial court denied Cordell’s motion to suppress the cocaine, ruling that, although the search was not conducted pursuant to a warrant, none was necessary as Cordell had consented to the search. Cordell was convicted of the charge after a bench trial, sentenced to a term of one year and one day, and further ordered to serve a special parole term of five years.
II.
A. The Airport Encounter
The district court found that Cordell’s consent to the search of his travel bag and the envelope containing the cocaine was voluntarily given. While the appellant testified that he withheld his consent to the search of the envelope, the trial judge did not credit his testimony. We do not understand Cordell’s argument on appeal to be that his consent was involuntary because it was given under coercion or duress. See Schneckloth v. Bustamonte, 412 U.S. 218, 219, 93 S.Ct. 2041, 2043, 36 L.Ed.2d 854 (1973). Rather, Cordell claims that he was *1285being illegally detained at the time the search was conducted, rendering the cocaine discovered in that search inadmissible against him as “the fruit of the poisonous tree.” See Wong Sun v. United States, 371 U.S. 471, 83 S.Ct. 407, 9 L.Ed.2d 441 (1963). The question, then, is whether at some point during the encounter, Cordell was being detained and, if so, whether the detention was constitutional.
Not all encounters between police officers and citizens implicate the provisions of the Fourth Amendment. In Florida v. Royer, _ U.S. _, 103 S.Ct. 1319, 75 L.Ed.2d 229 (1983), Justice White was joined by seven other justices in holding that:
Law enforcement officers do not violate the provisions of the Fourth Amendment by merely approaching an individual on the street or in another public place, by asking him if he is willing to answer some questions, by putting questions to him if the person is willing to listen, or by offering in evidence in a criminal prosecution his voluntary answers to such questions .... Nor would the fact that the officer identifies himself as a police officer, without more, convert the encounter into a seizure requiring some level of objective justification.
Id. 103 S.Ct. at 1324 (citations omitted). When officers O’Connor and Abreu identified themselves as police officers, asked Cordell if he would speak to them, and requested his identification and airline ticket, they were doing nothing that could be construed as a Fourth Amendment seizure unless one views all encounters between the police and citizens as seizures requiring justification, and we do not.
However, when O’Connor handed Cordell’s driver’s license and airline ticket to Abreu, and told Cordell they were conducting a narcotics investigation, the encounter had become a detention. The detention, though, never exceeded the boundaries of an investigatory stop. Id. at 1326. Thus the question we must answer is whether the officers had a reasonable, articulable suspicion of criminal activity — the standard of justification for investigatory stops. United States v. Brignoni-Ponce, 422 U.S. 873, 881-82, 95 S.Ct. 2574, 2580, 45 L.Ed.2d 607 (1975).
At the time they detained Cordell, the officers in this case did have a reasonable suspicion. Royer, 103 S.Ct. at 1326 (on facts similar to those here, eight justices agreed officers had reasonable suspicion justifying investigatory stop). In this case, Cordell had arrived from a major “source” city for narcotics. The names on his airline ticket and his driver’s license did not match. He had paid cash for his ticket. He appeared to be extremely nervous, and became more nervous as the officers continued to question him. Officers O’Connor and Abreu had been involved in narcotics investigations for seven and five years, respectively, and had been assigned to the O’Hare Task Force for well over a year. The officers clearly were “entitled to assess the facts in light of [their] experience,” Brignoni-Ponce, 422 U.S. at 885, 95 S.Ct. at 2582, and to suspect Cordell of a violation of the narcotics laws.
Finally, unlike the situation in Florida v. Royer, the detention in this case never matured into an arrest for which probable cause was needed. Royer was told he was under investigation for criminal activity, and taken to a small room while his baggage was retrieved, without his consent, from the airline. As Justice White noted for the plurality, “had Royer consented to a search on the spot [e.g., in the terminal where he was stopped], the search could have been conducted ... and any evidence recovered would have been' admissible against him.” 103 S.Ct. at 1328. In the instant case, Cordell did consent to a search “on the spot,” and the evidence discovered in the search was properly admitted against him.
B. The Sufficiency of the Evidence
Cordell also claims that the evidence against him was insufficient to establish his knowing possession of the cocaine found in his travel bag. We find no merit to this *1286claim. There is no question that Cordell arrived from Miami with approximately 240 grams of fifty-percent cocaine in his bag. Cordell maintained that a stranger in the Miami airport asked him to deliver the envelope containing the cocaine to Milwaukee, the city to which it was addressed. The return address on the envelope was fictitious. The Milwaukee address exists, but does not belong to “Joe Scott,” to whom the envelope was addressed. Beyond the question of how a stranger in the Miami airport would have known that Cordell, who was boarding a flight for Chicago, was ultimately to arrive in Milwaukee, we find it inherently incredible, as did the district court, that a stranger would entrust appellant with drugs worth close to $60,000. Appellant did not claim that he was not in knowing possession of the envelope itself; rath- ■ er, he claimed to be ignorant of its contents. Under these circumstances, there is more than enough evidence to establish Cordell’s knowledge.
III.
For the reasons expressed in the opinion, the judgment of conviction is affirmed.