delivered the opinion of the court:
Defendant Andres Roa appeals from his conviction for violation of section 401(a)(2)(A) of the Illinois Controlled Substances Act (720 ILCS 570/401(a)(2)(A) (West 2004)). On appeal, defendant raised the single issue of whether the trial court improperly denied his motion to suppress evidence seized during a consensual search of defendant’s vehicle. We affirmed the decision of the trial court on October 31, 2007. Defendant appealed to our supreme court which, in light of the postopinion case of People v. Cosby, 231 Ill. 2d 262 (2008), ordered this court to vacate its earlier judgment and reconsider its decision to determine if a different result is now warranted. People v. Roa, 229 Ill. 2d 687 (2008) (order). In light of Cosby, 231 Ill. 2d 262, we affirm the trial court’s decision.
BACKGROUND
Defendant was operating a vehicle he recently purchased when an Illinois state trooper stopped him for speeding at 71 miles per hour in a posted 65-mile-per-hour zone on Interstate 80 in Henry County, Illinois. The officer, Sergeant Floyd Blanks, is a certified drug interdiction instructor and the drug interdiction coordinator for his district. He has been employed by the State Police for 17 years.
According to the officer, after stopping defendant for speeding, he approached the car, advised defendant he was going to issue a written warning for speeding, and asked for defendant’s license and registration. Blanks stated that defendant fumbled for those documents, *160seemed “to exhibit more physical stress than most people do,” and mumbled while staring straight ahead. Blanks immediately advised defendant he was going to issue a written warning. At some point during the traffic stop, Blanks asked defendant where he was traveling from and where he was going. Defendant told Blanks that he was traveling from Colorado to New York.
Blanks said defendant seemed “to exhibit more physical stress than most people do, along with a couple of other factors.” Despite being informed that he was going to receive a warning, defendant remained nervous and, “in this case, that’s why I [Blanks] requested consent to search the vehicle.” Blanks also noticed a new air freshener and a strong odor of air freshener emanating from the car, which piqued Blanks’ suspicion.
According to Blanks, when he returned to his squad car to write a warning ticket, he knew, “with [defendant’s] nervousness, the odor of air freshener, *** [he] was going to try to obtain permission to search that vehicle.” Blanks testified, “I knew from my training and experience that something was amiss, something was wrong, so I requested assistance from Trooper Clint Thulen.”
Blanks did issue a written warning for the speeding violation. Once he delivered the written warning citation, Blanks returned defendant’s license, registration and insurance card. According to defendant, as the officer started to return to his squad car, the officer said, “Wait a minute, Andres,” and then asked defendant for permission to conduct a search of defendant’s car. Defendant consented.
According to Blanks, the conversation with defendant, before asking for consent, was slightly longer. The officer recounted that, after issuing a written warning and returning defendant’s license and insurance card, he asked defendant if everything in the vehicle belonged to him and whether anyone had asked defendant to transport anything. Defendant responded that everything in the vehicle belonged to him and no one had asked him to transport anything. Blanks then asked if there was anything illegal in the vehicle, including any alcohol, weapons, or drugs. The defendant replied, “no.” Blanks then asked if he could search the vehicle. Defendant’s response was, “yes.” According to Blanks, if defendant had refused permission to search his car, Blanks would have allowed him to drive away.
After obtaining consent, Blanks asked defendant what was in the trunk. Defendant answered, “antiques,” and offered to show him an antique dealer’s card. At Blanks’ request, defendant opened the trunk and found it was empty. Blanks felt this was unusual since defendant had just told him there were antiques in the trunk.
*161As requested, Trooper Thulen arrived on the scene during the initial moments of the search, while Blanks was standing near the trunk of defendant’s car. Together, the officers then proceeded to the front of the vehicle. Blanks noticed that the air bag area appeared to have been tampered with or modified. After a 20-minute search, which included using a fiberoptic scope, the officers discovered a hidden compartment containing cocaine. Later, when the compartment was disassembled, the troopers found the compartment contained a total of 24.2 pounds of cocaine. The cocaine was packaged in 11 separate packages.
Initially, defendant faced three charges based on this evidence. Count I alleged defendant knowingly brought more than 900 grams of cocaine into the State of Illinois with the intent to deliver in violation of section 401.1(a) of the Illinois Controlled Substances Act (Act) (720 ILCS 570/401.1(a) (West 2004)). Count II alleged defendant knowingly possessed with the intent to deliver more than 15 but less than 100 grams of cocaine in violation of section 401(a)(2)(A) of the Act (720 ILCS 570/401(a)(2)(A) (West 2004)). Finally, count III alleged that defendant possessed more than 900 grams of cocaine in violation of section 402(a)(2)(D) of the Act (720 ILCS 570/402(a)(2)(D) (West 2004)).
Prior to trial, defense counsel filed a motion to suppress the cocaine, alleging the police expanded a traffic stop into a drug investigation without probable cause. During the hearing on the motion, the trial court heard testimony from Sergeant Blanks regarding factors he considers when looking for drug-related activities. According to Blanks, ongoing nervousness is only one of many factors indicating illegal activity. Blanks explained to the court:
“There are a number of things that we are trained to observe, such as third-party vehicles, vehicles rented by someone else, the odor of air freshener and masking agents in the vehicle, a vehicle that looks lived in, a vehicle with numerous energy drinks or coffee cups showing they’ve been driving all night, cigarettes and nervousness, and I could go on and on, sir.”
Trooper Clint Thulen also testified at the suppression hearing. Thulen testified that he has been employed by the State Police for 14 years as a patrol officer and currently as a canine handler. When Thulen arrived on the scene of the stop, Blanks was searching defendant’s trunk. According to Thulen, defendant appeared unusually nervous and exhibited signs of stress. Defendant seemed unusually uncomfortable, “out of sorts,” and avoided eye contact.
Following the testimony of defendant, Sergeant Blanks and Trooper Thulen and arguments of counsel, the trial court denied the *162motion to suppress, finding Sergeant Blanks’ search was properly based on three grounds. First, the court noted Sergeant Blanks had probable cause for the initial traffic stop based on speeding. Second, the court found the duration of the traffic stop was reasonable because Sergeant Blanks did not delay asking for consent to search. Finally, the judge concluded, based on the totality of the circumstances, Sergeant Blanks had a reasonable, articulable suspicion that defendant was engaged in criminal conduct.
Applying a totality-of-the-circumstances approach, the court considered the officer’s description of the circumstances the officer encountered. Relevant factors included defendant’s extreme nervousness, mumbling, fumbling, straightforward gaze, abnormal physical stress, and a new air freshener that piqued the officer’s curiosity and suspicion. The court heavily weighed Sergeant Blanks’ vast experience in drug interdiction, finding Sergeant Blanks’ training would give a person in his position a reasonable, articulable suspicion that there was some kind of criminal activity afoot. Accordingly, the trial court denied defendant’s motion to suppress evidence.
Defendant’s first jury trial resulted in a deadlocked jury. Subsequently, the State dismissed counts I and III of the information and, following a stipulated bench trial on count II only, the trial judge found defendant guilty of unlawful possession with intent to deliver more than 15 grams but not more than 100 grams of a controlled substance, in violation of section 401(a)(2)(A) (720 ILCS 570/401(a)(2)(A) (West 2004)). The court sentenced defendant to 15 years’ imprisonment. Following the denial of his posttrial motions, defendant timely appealed on the ground that his motion to suppress should have been granted.
This court issued an opinion in this case on October 31, 2007, affirming the decision of the trial court, and defendant then filed an appeal with our supreme court. On December 31, 2008, the supreme court denied defendant’s leave to appeal, but entered a supervisory order requiring this court to vacate its prior judgment, in light of a postopinion case of People v. Cosby, 231 Ill. 2d 262 (2008), and directed this court to “reconsider its judgment *** to determine if a different result is warranted.” Roa, 229 Ill. 2d 687.
ANALYSIS
The State, after remand from our supreme court, asserts the police officer’s request for a consent to search defendant’s vehicle did not constitute a seizure under the fourth amendment according to the holding in Cosby. Defendant, after remand, contends that defendant did not feel free to leave when Sergeant Blanks asked for consent to *163search the vehicle. Consequently, defendant argues that the conversation following the end of the traffic stop created a second seizure of defendant. Defendant further contends that this court must now adhere to the view that a second seizure occurred because this premise was adopted by the author in our earlier decision and then mirrored in Justice McDade’s dissent to that decision.
We begin with defendant’s contention that we are bound by the premise that a second seizure occurred in this case when the officer requested consent to search defendant’s vehicle. This argument ignores that our supreme court issued a supervisory order with directions to this court to reconsider our judgment in light of the most recent pronouncement of law from our supreme court contained in Cosby. Cosby, 231 Ill. 2d 262.
This court’s previous decision, now under review, was based, in part, upon our supreme court’s decision in People v. Gonzalez, 204 Ill. 2d 220 (2003), which focused on the scope of the stop. The Gonzalez court originally pronounced a two-prong approach for determining whether a lawful traffic stop could become constitutionally impermissible by unduly prolonging the detention or by fundamentally altering the nature of the stop. Gonzalez, 204 Ill. 2d at 235. The Cosby court noted that the decision in Muehler v. Mena, 544 U.S. 93, 161 L. Ed. 2d 299, 125 S. Ct. 1465 (2005), struck down the approach that focused on the alteration of the fundamental nature of the stop previously employed by our supreme court. See Cosby, 231 Ill. 2d at 276, citing People v. Harris, 228 Ill. 2d 222, 240 (2008). In Harris, our supreme court held that Gonzalez, 204 Ill. 2d at 220, has been “unequivocally overruled” by the Supreme Court’s subsequent decision in Muehler. Harris, 228 Ill. 2d at 240.
Although the duration prong clearly survives based upon Illinois v. Caballes, 543 U.S. 405, 160 L. Ed. 2d 842, 125 S. Ct. 834 (2005), the alteration of the scope of the stop is no longer an appropriate consideration. Harris, 228 Ill. 2d at 240. Based upon the changes in the law since our first opinion, we reject defendant’s contention that we are bound by our initial holding regarding a second seizure, which was based on case law that has since been interpreted and modified by other higher courts.
Generally, the review of a trial court’s ruling on a motion to suppress involves a two-part standard of review, which presents mixed questions of law and fact. Cosby, 231 Ill. 2d at 271; People v. Luedemann, 222 Ill. 2d 530, 542 (2006). The reviewing court first examines whether the trial court’s factual findings are against the manifest weight of the evidence. Luedemann, 222 Ill. 2d at 542. Second, we review de novo the trial court’s ultimate ruling as to whether suppression is warranted. Harris, 228 Ill. 2d at 230.
*164As directed by our supreme court, we have vacated our prior judgment in this case and now must determine if a different outcome is warranted based on Cosby. The Cosby court analyzed the question of whether a consent to search after a traffic stop becomes a seizure by applying the principles set forth in its earlier case of People v. Brownlee, 186 Ill. 2d 501 (1999), and the United States Supreme Court’s decision in United States v. Mendenhall, 446 U.S. 544, 64 L. Ed. 2d 497, 100 S. Ct. 1870 (1980). Cosby, 231 Ill. 2d at 276-77. The Cosby case involved two consolidated cases for purposes of the appeal to the supreme court: People v. Cosby, No. 100681, and People v. Mendoza, No. 102584. In both cases, our supreme court determined that none of the Mendenhall factors were present and, therefore, fourth amendment seizures of the defendants did not occur. Cosby, 231 Ill. 2d at 282-88.
Following the decision in Cosby, the mandates of Mendenhall are even clearer and the holding of Brownlee remains intact. In Brownlee, our supreme court acknowledged that an officer is always free to request permission to search. Brownlee, 186 Ill. 2d at 515, citing Ohio v. Robinette, 519 U.S. 33, 136 L. Ed. 2d 347, 117 S. Ct. 417 (1996). However, our supreme court noted that a person is seized when, in view of all the facts and circumstances, he would not feel free to leave. Brownlee, 186 Ill. 2d at 517.
Questioning of a seized individual alone may not unduly prolong a stop or constitute an additional seizure within the meaning of the fourth amendment. Harris, 228 Ill. 2d at 243, citing Muehler, 544 U.S. at 101, 161 L. Ed. 2d at 309, 125 S. Ct. at 1471. Thus, we must apply the Mendenhall factors to determine if the questioning by Blanks, after issuing the warning ticket, would cause a reasonable person to feel he was not free to leave. Harris, 228 Ill. 2d at 243. The Mendenhall factors include: (1) whether there was a threatening presence by several officers; (2) whether the officer displayed a weapon; (3) whether there was some physical touching by the officer; and (4) whether the language or tone of voice used by the officer indicated that compliance with the officer’s request was compelled. Mendenhall, 446 U.S. at 554, 64 L. Ed. 2d at 509, 100 S. Ct. at 1877.1
First, Sergeant Blanks was the only officer present at the stop when the questioning regarding consent to search took place. Second, the officer did not display his weapon in a threatening manner. Third, *165there was no indication that the officer physically touched defendant. Finally, in reviewing the record, we find there is nothing to suggest that the officer used forceful language or an intimidating tone when communicating with defendant and requesting defendant’s permission to search his vehicle. Accordingly, in the absence of all of the Mendenhall factors as applied to the facts in the instant case, we find that defendant was not seized for purposes of the fourth amendment. See Cosby, 231 Ill. 2d at 287-88.
Next, we consider whether the four questions posed by Sergeant Blanks in this case unduly prolonged the encounter in violation of the fourth amendment. The record shows Blanks, after issuing the warning and returning the paperwork to defendant, immediately posed three questions that were short, succinct, and formulated to produce “yes” or “no” responses. The fourth and final question from the officer produced defendant’s voluntary consent for the officer to conduct a search. These questions were similar in nature to the questions asked by the officers in Cosby. Therefore, we conclude the inquiries by Blanks did not unfairly convert this lawful stop into an unconstitutional seizure of defendant or his vehicle.
There are three tiers of lawful police-civilian encounters: (1) arrests supported by probable cause; (2) brief investigatory detentions, justified by a reasonable, articulable suspicion of criminal activity (Terry v. Ohio, 392 U.S. 1, 20 L. Ed. 2d 889, 88 S. Ct. 1868 (1968)); and (3) consensual encounters involving no coercion or detentions that do not implicate fourth amendment interests. Luedemann, 222 Ill. 2d at 544. Here, the initial traffic stop was based upon probable cause to believe defendant was speeding.
Originally, in his special concurring opinion, Presiding Justice Lytton concluded the police-citizen interaction after the officer delivered the written warning qualified as a third-tier “consensual encounter” under Luedemann, 222 Ill. 2d at 544. People v. Roa, 377 Ill. App. 3d 190, 205 (2007) (Lytton, P.J., concurring). The decision in Cosby reveals Justice Lytton was correct. In light of Cosby, we are now in agreement that Blanks’ request for consent to search was constitutionally permissible under the fourth amendment as a third-tier consensual encounter.
While defendant admits his decision to give Sergeant Blanks his consent to search was voluntary, on remand defendant alleges Blanks waited several additional minutes for Officer Thulen to arrive. Defendant also argues that his consent to search was limited in scope. The record reflects that Sergeant Blanks testified defendant consented to his search of the “vehicle” and that he began the search before the arrival of Officer Thulen.
The conflict in the testimony required the trial court to make a credibility determination regarding the duration of the stop and the *166scope of the consent. Matters of credibility are for the trial court to decide. This court should not rule on such matters because the trial court was in a position to observe the witnesses, assess their demeanor, and make credibility judgments based on a firsthand encounter with the witnesses. People v. Hornsby, 277 Ill. App. 3d 227, 230-31 (1995). Here, the record sustains the trial court’s finding that Blanks was a credible witness. We conclude the court’s findings were not against the manifest weight of the evidence simply because the circumstances that triggered the officer’s suspicion involved multiple layers of conduct which, standing alone, could be considered as innocent, law-abiding behavior.
As stated in our prior opinion, effective and efficient interstate drug couriers can successfully avoid apprehension by camouflaging their illegal activity with something as innocuous as an air freshener. Meaningless minutiae that might go unnoticed by the untrained person may become a significant factor to an experienced drug interdiction officer considering the totality of the circumstances attendant to the traveler at hand. The trial judge found the officer’s testimony credible and the basis of his suspicions justified.
Pursuant to the directive of our supreme court, we vacate our previous judgment in this case. Additionally, based upon our de novo review of the facts as applied to the most recent case law, we hold the motion to suppress contraband was properly denied because defendant’s interaction with Officer Blanks, after receiving the written warning, was voluntary and consensual. Accordingly, we affirm the circuit court’s decision to deny defendant’s motion to suppress evidence seized from his vehicle.
CONCLUSION
The judgment entered in this case on October 31, 2007, has been vacated. Additionally, after reconsidering our previous decision in light of Cosby as directed by the supervisory order of our supreme court, we affirm the order of the circuit court of Henry County denying defendant’s motion to suppress the evidence obtained from the consensual search.
Affirmed.
LYTTON, J., concurs.