ALTIMARI, Circuit Judge:
Defendant-appellant Reginald Glover appeals from a judgment of conviction, entered in the United States District Court for the Western District of New York (Richard J. Arcara, Judge), finding him guilty of possession with the intent to distribute cocaine in violation of 21 U.S.C. § 841(a)(1) (1988).
The contraband forming the basis of Glover’s conviction was recovered from his luggage after an encounter between Glover and members of a Drug Enforcement Administration (“DEA”) Task Force at the Niagara Frontier Transit Authority (“NFTA”) bus terminal in Buffalo, New York. On appeal, Glover contends that his conviction should be reversed because the district court erred in concluding that his Fourth Amendment rights were not violated during the encounter and, consequently, in denying his motion to suppress the narcotics recovered from his suitcase. Specifically, Glover argues that the officers had no objective level of suspicion to justify [1006]*1006seizing him or his bags, thereby tainting the evidence found during the subsequent consensual search of his luggage.
For the reasons set forth below, we affirm the judgment of the district court.
BACKGROUND
For approximately the past one and one-half years, Investigator Paul Terranova of the Erie County Sheriffs Department and Agent William Spencer of the United States Border Patrol have been members of a DEA Task Force that enforces drug, immigration, and currency laws at the NFTA bus terminal and at other transportation centers in Buffalo. As part of their duties, Task Force members regularly observe passengers arriving on the early morning express bus from New York City. Interest in this particular bus is not accidental. As this Court previously has observed, “New York City is the principal source for drugs sold in western New York,” United States v. Montilla, 928 F.2d 583, 584 (2d Cir.1991), and the express bus is used by drug traffickers to transport narcotics to the Buffalo area. See United States v. Torres, 949 F.2d 606, 607 (2d Cir.1991); Montilla, 928 F.2d at 584. Indeed, the Task Force’s questioning of select express bus passengers yields approximately three to four arrests per month. Montilla, 928 F.2d at 584-85.
On May 16, 1990, Terranova and Spencer were on patrol at the NFTA bus terminal when the morning express bus arrived from New York City and parked at Gate 5. All of the passengers disembarked the bus and entered the terminal through Gate 5, except defendant-appellant Glover, who entered through Gate 4. Because Glover had separated himself from the main flow of traffic, Terranova and Spencer continued to observe him. They noticed that Glover appeared nervous, continually looked over his shoulders, and, though outside on a somewhat cool day, was the only passenger sweating from his face and brow. As he entered the terminal building carrying his two unchecked bags (a shoulder bag and a small suitcase), Glover walked extremely slowly and continually scanned the entire terminal area in a jerky fashion that Terra-nova believed was calculated to detect possible surveillance. Glover proceeded in this manner toward the terminal exit.
At that point, as a result of his observations, Terranova approached Glover, identified himself as a police officer, and asked if he could question Glover. Glover agreed to be questioned. During the subsequent questioning, Spencer stood silently several feet behind Terranova. Terranova began by asking Glover for identification. In response, Glover reached into his sock, retrieved his wallet, and handed Terranova a handwritten employee identification card. After asking Glover his name, Terranova requested additional identification. Glover produced a photocopied Social Security document with an illegible number. Terrano-va noticed that the identification Glover provided contained two different addresses.
Terranova then asked Glover why he was visiting Buffalo. Glover answered that he was in town to pay a surprise visit to his aunt. Because of the nature of the identification Glover provided — one handwritten, one illegible, and each with a different address — Terranova asked if he could phone Glover’s aunt to confirm his identification. Glover refused, stating that the phone call would ruin the surprise. Glover also refused to allow Terranova to phone his employer, explaining that his employer wrongly believed that Glover had taken a sick day. Throughout this encounter with Ter-ranova, Glover was sweating heavily, shaking nervously, and continually looking toward the exit.
Terranova then told Glover that he was concerned with drug smuggling in the Western New York area and asked Glover if he was carrying narcotics. Glover responded that he was not. Glover then refused Terranova’s request to search his bags, stating that Terranova did not have “probable cause” to search his luggage. While still holding Glover’s identification, Terranova asked if Glover would accompany him to the NFTA office for a further check on his identification. Glover agreed to go.
[1007]*1007When Glover, Terranova, and Spencer arrived at the NFTA office, which was located approximately thirty feet from the terminal exit, Glover was asked, among other things, his birth date and whether he had a criminal history. Glover stated that he was born on November 3,1968, and that he had no criminal history. Within minutes, a computer check of Glover’s identification revealed that Glover’s birthday was November 2, and that he had a criminal history of narcotics-related arrests and had used aliases. When asked to explain why he had lied regarding his criminal history, Glover responded that he believed Terranova’s question pertained only to crimes in the Buffalo area.
At that point, Glover again refused a request to have his bags searched. Terra-nova then informed Glover that his bags would be detained until a narcotics detection dog arrived to conduct a “sniff test.” Another agent present in the office told Glover that, although his bags would be detained, he was free to leave. The agent also told Glover that if the dog reacted positively to the bags, the officers would apply for a search warrant. Glover immediately refused to leave, insisting that he wanted to remain to make sure the officers obtained a warrant.
When the narcotics dog arrived, approximately thirty minutes had elapsed from the time Terranova had asked Glover to go to the NFTA office. In a controlled inspection involving several different pieces of luggage, the dog “hit on” Glover’s bags. Once informed of the dog’s reaction, Glover picked up his shoulder bag, threw it onto a desk, and told the officers to search it. After confirming that Glover wanted the bag searched, Terranova examined its contents and discovered a package containing a quantity of marijuana. At that point, Task Force Investigator June Bradley, who had entered the office, asked Glover if she could search his other bag. Glover responded “[y]ou might as well look in that one too.” After opening the bag, Bradley discovered a package containing a white powder that was subsequently determined to be cocaine. Glover was then arrested and subsequently charged with one count of possessing with the intent to distribute a controlled substance in violation of 21 U.S.C. § 841(a)(1).
In district court, Glover moved to suppress the marijuana and cocaine, arguing that the search of his luggage was undertaken following an encounter with the police that violated his Fourth Amendment rights. After a suppression hearing, Judge Arcara first concluded that the initial encounter between Glover and the officers was entirely consensual. The District Judge further found that by the time the officers seized Glover’s bags in the NFTA office by holding them for a “sniff test,” they clearly “had reasonable suspicion based on articulable facts that [Glover] was carrying contraband.” Finally, the court concluded that after the narcotics dog “hit on” Glover’s bags, Glover voluntarily consented to the search that yielded the drugs. Accordingly, the district court denied Glover’s motion to suppress. Glover subsequently entered a conditional plea of guilty, reserving his right to appeal the denial of his suppression motion. This appeal followed.
DISCUSSION
In considering a district court’s ruling on a suppression motion, this Court reviews the district court’s factual findings under a “clearly erroneous” standard, see, e.g., United States v. Springer, 946 F.2d 1012, 1015 (2d Cir.1991); United States v. Hooper, 935 F.2d 484, 489 (2d Cir.), cert. denied, — U.S. -, 112 S.Ct. 663, 116 L.Ed.2d 754 (1991); United States v. Montilla, 928 F.2d at 588, construing all of the evidence in the light most favorable to the government. See, e.g., United States v. Villegas, 928 F.2d 512, 517 (2d Cir.), cert. denied, — U.S. -, 112 S.Ct. 137, 116 L.Ed.2d 104 (1991); United States v. Jackson, 652 F.2d 244, 246 (2d Cir.), cert. denied, 454 U.S. 1057, 102 S.Ct. 605, 70 L.Ed.2d 594 (1981). “We review de novo questions of law such as whether a seizure occurred and, if so, whether reasonable suspicion justified it.” Springer, 946 F.2d at 1015; see also Hooper, 935 F.2d at 489; Montilla, 928 F.2d at 588.
[1008]*1008Our analysis begins with some preliminary observations. As we stated in Hooper, there are three types of encounters between police and individuals, each with different ramifications under the Fourth Amendment. See 935 F.2d at 490. The first type is a consensual encounter whereby an individual willingly agrees to speak to law enforcement personnel. See id. Such contact may be initiated by the police without any objective level of suspicion and does not, without more, amount to a “seizure” implicating the Fourth Amendment’s protections. See id.; see also Florida v. Bostick, — U.S. -, 111 S.Ct. 2382, 2386, 115 L.Ed.2d 389 (1991); Springer, 946 F.2d at 1016; United States v. Lee, 916 F.2d 814, 819 (2d Cir.1990). Discussing the parameters of such consensual encounters, the Supreme Court recently observed in Bostick that “even when officers have no basis for suspecting a particular individual, they may generally ask questions of that individual ...; ask to examine the individual’s identification ...; and request consent to search his or her luggage ... as long as the police do not convey a message that compliance with their requests is required.” 111 S.Ct. at 2386 (citations omitted).
The second type of encounter, based on the principles enunciated in Terry v. Ohio, 392 U.S. 1, 88 S.Ct. 1868, 20 L.Ed.2d 889 (1968), involves a limited investigative stop of an individual and/or his or her bags. See United States v. Sharpe, 470 U.S. 675, 682, 105 S.Ct. 1568, 1573, 84 L.Ed.2d 605 (1985); United States v. Place, 462 U.S. 696, 702, 103 S.Ct. 2637, 2642, 77 L.Ed.2d 110 (1983); see also Hooper, 935 F.2d at 490, 492-93. Although limited in scope, such investigative detentions are “seizures” under the Fourth Amendment, see, e.g., Hooper, 935 F.2d at 490, and must be based on “a reasonable suspicion supported by articulable facts that criminal activity ‘may be afoot.’ ” United States v. Sokolow, 490 U.S. 1, 7, 109 S.Ct. 1581, 1585, 104 L.Ed.2d 1 (1989) (quoting Terry, 392 U.S. at 30, 88 S.Ct. at 1884). The third and final type of encounter is an arrest— plainly a Fourth Amendment “seizure”— that must be based on probable cause. See, e.g., Hooper, 935 F.2d at 490; United States v. Bradley, 923 F.2d 362, 364 (5th Cir.1991).
To determine whether a “seizure” has occurred triggering the Fourth Amendment’s protections, a court must consider “ 'if, in view of all of the circumstances surrounding the [encounter], a reasonable person would have believed that he [or she] was not free to leave.’ ” Lee, 916 F.2d at 819 (quoting Michigan v. Chesternut, 486 U.S. 567, 573, 108 S.Ct. 1975, 1979, 100 L.Ed.2d 565 (1988) (quoting United States v. Mendenhall, 446 U.S. 544, 554, 100 S.Ct. 1870, 1877, 64 L.Ed.2d 497 (1980) (opinion of Stewart, /.))); see also Bostick, 111 S.Ct. at 2389. The test is an objective one, see, e.g., Springer, 946 F.2d at 1016; Lee, 916 F.2d at 819, based on how a reasonable innocent person would view the encounter. Bostick, 111 S.Ct. at 2388. As a guide to applying this test, we have enumerated certain factors that might suggest that a seizure occurred, namely:
the threatening presence of several officers; the display of a weapon; the physical touching of the person by the officer; language or tone indicating that compliance with the officer was compulsory; prolonged retention of a person’s personal effects, such as airplane tickets or identification; and a request by the officer to accompany him to the police station or a police room.
Lee, 916 F.2d at 819; see also Mendenhall, 446 U.S. at 554, 100 S.Ct. at 1877 (opinion of Stewart, J.); Springer, 946 F.2d at 1016.
In the present case, applying the applicable legal standard, the district court found that Glover’s bags were seized when, once in the NFTA office, Terranova told Glover that his bags would be detained pending the arrival of a narcotics dog. Until that point, the court found that the entire encounter was consensual. The district court raised, but did not decide, the issue of whether Glover was also seized at that point, despite being told that he was free to leave. Rather, the court observed that whether Glover was seized was not pertinent because the same standards applied in [1009]*1009determining the constitutionality of detaining him as well as his bags. Moreover, the court found that the investigative detention of Glover and his bags was supported by reasonable suspicion that he was carrying narcotics. Challenging the court’s conclusions, Glover contends that the seizure occurred earlier, when Terranova, still retaining Glover’s identification, asked Glover to accompany him to the NFTA office for further questioning. According to Glover, the officers did not then, or at any other time during the encounter, have reasonable suspicion to justify a Terry-type investigative detention of him or his bags.
Initially, we note that prior to the time Terranova asked Glover to return to the NFTA security office, the encounter was consensual. Although accompanied by Spencer, Terranova alone approached Glover in a public place, identified himself as a police officer, and, in a non-threatening manner, asked Glover certain questions, requested identification, and asked whether Glover would consent to have his bags searched for narcotics. No weapons were displayed and there was no physical contact between the officers and Glover. Under these circumstances, it is plain that no seizure had occurred. See, e.g., Bostick, 111 S.Ct. at 2386, 2388; Springer, 946 F.2d at 1016-17; Hooper, 935 F.2d at 492; Lee, 916 F.2d at 819.
However, when Terranova requested Glover to leave the public area of the terminal and to return to the NFTA security office for further questioning, without returning Glover’s identification and without telling Glover that he was free to leave, we believe that Glover and his bags were seized. See Florida v. Royer, 460 U.S. 491, 501, 103 S.Ct. 1319, 1326, 75 L.Ed.2d 229 (1983) (plurality opinion) (once “officers identified themselves as narcotics agents, told [defendant] he was suspected of transporting narcotics, and asked him to accompany them to the police room, while retaining his ticket and driver’s license and without indicating in any way that he was free to depart, [defendant] was effectively seized”). Standing alone, Terranova’s failure to advise Glover that he was free to terminate the interview and leave would not turn an otherwise consensual encounter into a seizure. See, e.g., Springer, 946 F.2d at 1016. However, we believe that failure, combined with the failure to return Glover’s identification and the request to accompany the officers to a police room, amounted to a seizure because under such circumstances, a reasonable person would not have felt free to leave. Compare Royer, 460 U.S. at 501-02, 103 S.Ct. at 1326 with Torres, 949 F.2d at 608 (request to accompany officers to police office, without more, did not establish seizure); see also Lee, 916 F.2d at 819 (factors which indicate a seizure occurred include an officer’s retention of an individual’s identification and a request to accompany the officer to a police office).
Our conclusion that a seizure occurred at that point in Glover’s encounter with the officers does not, however, end our inquiry. Rather, we must consider whether there existed a reasonable suspicion that Glover was carrying narcotics to justify a limited detention of Glover and his bags and, if so, whether the officers’ conduct exceeded the scope of a permissible investigative stop. See Place, 462 U.S. at 706-710, 103 S.Ct. at 2644-46; Royer, 460 U.S. at 498-500, 103 S.Ct. at 1325; Hooper, 935 F.2d at 492-94.
To justify a limited Terry-type investigative stop, a law. enforcement officer must have a reasonable suspicion based on articulable facts that the suspect “is, has been, or is about to be engaged in criminal activity.” Villegas, 928 F.2d at 516; see also Sokolow, 490 U.S. at 7, 109 S.Ct. at 1585; Terry, 392 U.S. at 30, 88 S.Ct. at 1884; Hooper, 935 F.2d at 493. Although the concept of reasonable suspicion is not susceptible to precise definition, see, e.g., Sokolow, 490 U.S. at 7, 109 S.Ct. at 1585; Hooper, 935 F.2d at 493, the requisite level of suspicion to make an investigative stop is “ ‘considerably less than proof of wrongdoing by a preponderance of the evidence.’ ” Villegas, 928 F.2d at 516 (quoting Sokolow, 490 U.S. at 7, 109 S.Ct. at 1585). Still, “[t]he Fourth Amendment requires ‘some minimal level of objective [1010]*1010justification’ for making the stop.” Sokolow, 490 U.S. at 7, 109 S.Ct. at 1585 (quoting INS v. Delgado, 466 U.S. 210, 217, 104 S.Ct. 1758, 1763, 80 L.Ed.2d 247 (1984)). Consequently, an officer’s inchoate suspicion or mere hunch is insufficient to justify a Terry-type detention. Sokolow, 490 U.S. at 7, 109 S.Ct. at 1585 (citing Terry, 392 U.S. at 27, 88 S.Ct. at 1883).
The standard for determining whether a particular stop was justified by reasonable suspicion is an objective one, see, e.g., United States v. Salazar, 945 F.2d 47, 49 (2d Cir.1991); Villegas, 928 F.2d at 516; United States v. Nersesian, 824 F.2d 1294, 1316 (2d Cir.), cert. denied, 484 U.S. 958, 108 S.Ct. 357, 98 L.Ed.2d 382 (1987), not dependent on the intentions or motivations of the particular detaining officers. See, e.g., Nersesian, 824 F.2d at 1316. In the case of suspected narcotics trafficking, an officer’s suspicion will be reasonable if, considering the totality of the circumstances surrounding the stop, “the conduct would appear suspect to one familiar with the practices of narcotics couriers, albeit the pattern of behavior is innocuous to the untrained observer.” Villegas, 928 F.2d at 516 (citation omitted); see also United States v. Price, 599 F.2d 494, 501 (2d Cir.1979).
In the present case, at the point when Terranova asked Glover to return to the NFTA security office, the district court found, among other things, that Glover was traveling to Buffalo from New York City, a “source city” of narcotics for western New York. In particular, he was traveling on the early morning express bus, which has been used by drug couriers to transport narcotics to the Buffalo area. See Torres, 949 F.2d at 607; Mantilla, 928 F.2d at 584. As he exited the bus, Glover was sweating from his face and brow and was looking around nervously over his shoulders as he entered the NFTA terminal. Moreover, although all of the other passengers on the bus entered the terminal through Gate 5, where the bus had parked, Glover separated himself from the mainstream and entered the terminal alone through Gate 4, some twenty to thirty feet away. As Glover entered the terminal, Terranova and Spencer observed that he walked in an extremely slow manner, continually scanning the entire terminal area in quick, jerky movements, apparently designed to detect possible surveillance.
After Terranova approached Glover, identified himself, and asked for identification, Glover produced from his sock two pieces of identification: one handwritten employee identification card and one photocopied Social Security document with a partially obliterated number. Each piece of identification bore a different address. When asked why he was in Buffalo, Glover responded that he was paying a surprise visit to his aunt. Glover refused to allow Terranova to contact his aunt to verify his identification, explaining that to do so would ruin his surprise. He also refused to allow Terranova to contact his employer because although Glover allegedly took a sick day, he was really on vacation. Moreover, throughout the encounter, Glover was sweating heavily and shaking nervously.
These factual findings are supported by the record and are not “clearly erroneous.”1 See, e.g., Hooper, 935 F.2d at 489; Villegas, 928 F.2d at 517. Glover essentially argues, however, that each of these facts, even if true, is innocuous and fails to support a finding of reasonable suspicion. We disagree. Even conduct seemingly innocent may form the basis for reasonable suspicion that criminal activity is afoot. Sokolow, 490 U.S. at 9, 109 S.Ct. at 1586 (citation omitted). Here, although each fact viewed separately may be consistent with innocent travel, we believe that Glover’s overall conduct, viewed objectively [1011]*1011by an officer familiar with drug courier practices, see, Villegas, 928 F.2d at 516, gave rise to a reasonable suspicion that Glover was transporting narcotics, thereby warranting the detention of Glover and his bags for further investigation. See Sokolow, 490 U.S. at 9-10, 109 S.Ct. at 1586-87; Mendenhall, 446 U.S. at 560-61, 564-65, 100 S.Ct. at 1880, 1882 (Powell, J, concurring); Torres, 949 F.2d at 608; Springer, 946 F.2d at 1017; Hooper, 935 F.2d at 493; Lee, 916 F.2d at 820.
Having determined that there existed reasonable suspicion to justify an investigative stop, we must next consider whether the officers’ actual conduct fell within the permissible scope of a Terry-type detention. For an investigative stop based on reasonable suspicion to pass constitutional muster, the ensuing investigation must be reasonably related in scope and duration to the circumstances that justified the stop in the first instance, so as to be minimally intrusive of the individual’s Fourth Amendment interests. See Sharpe, 470 U.S. at 685-86, 105 S.Ct. at 1575; Place, 462 U.S. at 706, 709, 103 S.Ct. at 2644, 2645; Royer, 460 U.S. at 500, 103 S.Ct. at 1325. If an investigative stop based on reasonable suspicion continues too long or becomes unreasonably intrusive, it will ripen into a de facto arrest that must be based on probable cause. See Sharpe, 470 U.S. at 685, 105 S.Ct. at 1575; Hooper, 935 F.2d at 494.
A critical factor in evaluating the intrusiveness of a stop is the length of the detention. See, e.g., Sharpe, 470 U.S. at 675-76, 105 S.Ct. at 1570; Place, 462 U.S. at 709, 103 S.Ct. at 2645; Hooper, 935 F.2d at 495. No bright-line rule exists, however, to determine the outer time limit of a permissible Terry-type stop. See, e.g., Place, 462 U.S. at 709, 103 S.Ct. at 2645. Rather, in considering the reasonableness of the duration of a particular detention, a court must “examine whether the police diligently pursued a means of investigation that was likely to confirm or dispel their suspicions quickly, during which time it was necessary to detain the defendant.” Sharpe, 470 U.S. at 686, 105 S.Ct. at 1575; see also Place, 462 U.S. at 709, 103 S.Ct. at 2645. In making this inquiry, the Supreme Court has cautioned that a court should not “ ‘indulge in unrealistic second-guessing’ as to the means law enforcement officers ... employ to conduct their investigations.” Hooper, 935 F.2d at 497 (quoting Sharpe, 470 U.S. at 686, 105 S.Ct. at 1575); see also United States v. Alexander, 907 F.2d 269, 273 (2d Cir.1990), cert. denied, — U.S. -, 111 S.Ct. 983, 112 L.Ed.2d 1067 (1991). “The question is not simply whether some ... alternative [method] was available, but whether the police acted unreasonably in failing to recognize or pursue it.” Sharpe, 470 U.S. at 687, 105 S.Ct. at 1576; see also Alexander, 907 F.2d at 273. We observe further that the standards applicable to assessing the propriety of such Terry-type stops apply equally to the detention of individuals and/or their luggage or other personal effects. See Place, 462 U.S. at 708-09, 103 S.Ct. at 2645; United States v. Sterling, 909 F.2d 1078, 1084 (7th Cir.1990).
Relying principally on Royer, 460 U.S. at 503, 103 S.Ct. at 1327, Glover contends that his detention in the NFTA office was a de facto arrest. Glover also argues that the detention of his bags exceeded the permissible boundaries of the Fourth Amendment. We find these contentions unpersuasive.
In Royer, officers approached the defendant Royer, a suspected narcotics courier, in. an airport, questioned him, obtained his airline tickets and identification, told him he was suspected of drug smuggling, and asked him to accompany them to a police room. Once in the room, the officers proceeded with their investigation and retrieved Royer’s luggage from the airline without his consent, all without ever telling Royer that he was free to leave and catch his plane. In a plurality opinion, the Supreme Court held that under such circumstances, Royer was effectively under arrest. See 460 U.S. at 503, 103 S.Ct. at 1327. In support of this conclusion, the plurality scrutinized the means of investigation used by the agents and found that they were overintrusive under the circumstances. Among other things, the Court noted that the record reflected that no le[1012]*1012gitimate law enforcement purposes were served by asking Royer to go to the security office. Id. at 505, 103 S.Ct. at 1328. In addition, the Court found that the officers could have, but failed to, use a narcotics dog to perform a “sniff test” on the defendant’s bags, which could have resulted in only a momentary detention. Id. at 505-06, 103 S.Ct. at 1328-29. Although perhaps not dispositive, the Court buttressed its conclusion that Royer was subject to a de facto arrest by indicating that the State had conceded in the lower courts that Roy-er would not have been free to leave. Id. at 503, 103 S.Ct. at 1327.
We do not read Royer as establishing a per se rule that moving from an airport, bus, or train terminal to a police office during a Terry-type encounter, for purposes of further investigation, automatically converts an otherwise permissible stop into an impermissible arrest upon arrival at the office. See, e.g., United States v. Knox, 839 F.2d 285, 290-91 (6th Cir.1988), cert. denied, 490 U.S. 1019, 109 S.Ct. 1742, 104 L.Ed.2d 179 (1989); United States v. Borrero, 770 F.Supp. 1178, 1190-91 (E.D.Mich.1991). Rather each case must be evaluated on its facts to determine whether a particular seizure is justified on grounds of reasonable suspicion. See Sharpe, 470 U.S. at 685-86, 105 S.Ct. at 1575; see also Royer, 460 U.S. at 506-07, 103 S.Ct. at 1329.
Under the circumstances of this case, we do not believe that Glover’s detention ripened into a full-blown arrest. Royer is plainly distinguishable. First, unlike the officers in Royer, Terranova and Spencer had a legitimate law enforcement purpose in asking Glover to return to the NFTA office. Once there existed reasonable suspicion that Glover was engaged in narcotics activity, the officers were justified in conducting a computer check to verify the accuracy of his rather dubious and facially unreliable identification — a handwritten employment card and a photocopied Social Security document with an illegible number. In hindsight, it may be that they somehow could have verified Glover’s identification without asking him to return to the office. However, considering the nature of the identification, his refusal to allow them to verify the information with his aunt or his employer, and the other factors contributing to the existence of reasonable suspicion, we do not believe that the officers’ chosen course of conduct was unreasonable. See Sharpe, 470 U.S. at 686-87, 105 S.Ct. at 1575-76; see also Hooper, 935 F.2d at 497.
Second, and more importantly, unlike the defendant in Royer, Glover was expressly told that he was free to leave the office, though his bags would have to be detained pending the dog’s arrival. See Dunaway v. New York, 442 U.S. 200, 212, 99 S.Ct. 2248, 2256, 60 L.Ed.2d 824 (1979) (factor in determining whether suspect under arrest is whether he is told he is free to go). Rather than leave, however, Glover chose to remain in order to ensure that the officers obtained a warrant. At that point, Glover knew that a narcotics dog was on the way and that, depending on the dog’s reaction, his detention could be over in “short order.” Royer, 460 U.S. at 504, 103 S.Ct. at 1328. Although the officers still had Glover’s identification and indicated that they would detain his luggage until the dog arrived, once Glover was told he was free to leave, he was, under the circumstances of this case, plainly not under arrest.
Not only was Glover not under arrest, but he was arguably no longer “seized” for Fourth Amendment purposes. While the officers failed to tell Glover specifically how to retrieve his luggage if he chose to leave — a practice we do not encourage, see Place, 462 U.S. at 708 & n. 8, 710, 103 S.Ct. at 2645 & n. 8, 2646 — given Glover’s reason for remaining, i.e., to monitor the officers’ conduct, we cannot say that their failure to instruct Glover on how to recover his luggage if the “sniff test” proved negative caused him to stay so as to effectively continue his seizure. Moreover, with regard to Glover’s identification, we believe that, once told he was free to leave, a reasonable person under the circumstances would simply have requested the officers to return his identification.
[1013]*1013Even assuming, however, that Glover remained seized under the Fourth Amendment, despite being told that he was free to leave, see id., we do not believe that detaining him along with his bags until the arrival of the narcotics dog converted an otherwise permissible detention based on reasonable suspicion into an arrest requiring probable cause. Upon returning to the NFTA office, the officers’ acted diligently and in a non-threatening manner to confirm or dispel their suspicions that Glover was engaged in narcotics trafficking. They promptly conducted a computer check to verify Glover’s identification, and learned, contrary to Glover’s representations, that he had prior narcotics convictions, had also used aliases, and had given an incorrect birthdate. Once Glover refused consent to search his bags, the officers immediately arranged for the narcotics dog, which arrived about twenty minutes later. Both the computer search and the dog sniff were minimally intrusive means of confirming or dispelling the officers’ suspicion. See Place, 462 U.S. at 707, 103 S.Ct. at 2644 (“sniff test” minimally intrusive).
Moreover, calculated from the moment Glover and his bags were initially seized until the arrival of the narcotics dog, approximately thirty minutes had elapsed. Part of this time was used to clarify Glover’s misrepresentations regarding his background. Given the officer’s diligence in pursuing their investigation, and given the Government’s substantial interest in drug interdiction, see, e.g., Place, 462 U.S. at 703, 103 S.Ct. at 2642 (citing Mendenhall, 446 U.S. at 561, 100 S.Ct. at 1880 (Powell, J., concurring)); Hooper, 935 F.2d at 498, detaining Glover for approximately thirty minutes with his bags to conduct brief questioning and to await the arrival of the narcotics dog was a limited intrusion on Glover’s Fourth Amendment interests wholly justified by reasonable suspicion. See United States v. Mondello, 927 F.2d 1463, 1471 (9th Cir.1991) (thirty minute detention of defendant and his luggage inside his private plane while drug agents arranged for narcotics dog to inspect defendant’s luggage held reasonable); Knox, 839 F.2d at 290-91 (thirty minute detention in airport security office of defendants and their luggage followed by “sniff test” held reasonable); Borrero, 770 F.Supp. at 1189-91 (seventy minute detention in security office, due in part to necessity for translation, prior to performance of “sniff test” held reasonable); cf. United States v. Sullivan, 903 F.2d 1093, 1097-98 (7th Cir.1990) (forty-five minute detention of luggage for “sniff test” held reasonable).
Accordingly, we conclude that the officers’ investigative stop of Glover and his bags was a permissible Terry-type detention founded on a reasonable suspicion that Glover was engaged in narcotics trafficking. Although we uphold the investigative stop of Glover and his bags on somewhat different grounds than those relied upon by the district court, it is well-settled that a reviewing court “may affirm ‘on any grounds for which there is a record sufficient to permit conclusions of law, including grounds not relied upon by the district court.’ ” Chesley v. Union Carbide Corp., 927 F.2d 60, 68 (2d Cir.1991) (citation omitted).
Finally, once the narcotics dog “hit on” Glover’s bags, the police had probable cause to obtain a search warrant. See, e.g., Royer, 460 U.S. at 506, 103 S.Ct. at 1329; United States v. Waltzer, 682 F.2d 370, 374 (2d Cir.1982), cert. denied, 463 U.S. 1210, 103 S.Ct. 3543, 77 L.Ed.2d 1392 (1983). Glover, however, consented to a search of his bags before a warrant was obtained. Although not challenged by Glover on appeal, we agree with the district court’s conclusion that the warrantless seizure of the contraband from Glover’s bags following the “sniff test” was proper because, under the totality of the circumstances, Glover’s consent to the search was entirely voluntary. See, e.g., United States v. Watson, 423 U.S. 411, 424-25, 96 S.Ct. 820, 828, 46 L.Ed.2d 598 (1976); Schneckloth v. Bustamonte, 412 U.S. 218, 219, 93 S.Ct. 2041, 2043, 36 L.Ed.2d 854 (1973); Price, 599 F.2d at 503.
CONCLUSION
Based on the foregoing, the judgment of the district court is affirmed.