James A. Almand was charged with possession of 550 pounds of marijuana with intent to distribute, in violation of 21 U.S.C. § 841(a)(1). He waived trial by jury, moved unsuccessfully to suppress the seized marijuana, and was convicted and sentenced. He asserts on appeal that no reasonable grounds existed for his initial interrogation by the Border Patrol, and that consent to the search of his parked camper was lacking. We find no merit in his contentions and affirm.
I. FACTS
Around 6:00 a. m. on January 22, 1976, a Border Patrol radio operator at the Marfa, Texas, Control Center received signals in sequence from sensor devices located on Highway 170, near Study Butte, indicating that a vehicle was proceeding northeast through Big Bend National Park toward Highway 385. The radio operator notified Border Patrolman Wilson at his home in Alpine, Texas. The location of the vehicle and the time of day indicated to Wilson a possibility of alien smuggling from the un-patrolled river area to the southwest on Highway 170, a distance of about six miles from the first sensor. Wilson telephoned his fellow officer Smith, who agreed to accompany Wilson in an investigation. The officers drove down Highway 90 at speeds in excess of 100 mph, hoping to intercept the vehicle on Highway 385 a few miles south of Marathon, Texas. By maintaining contact with the radio operator, Wilson and Smith learned that the last sensor activated, no. 317, was some 35 miles south of Marathon on Highway 385 and that the other sensors north of no. 317 had not been tripped, leading Wilson and Smith to believe the vehicle had stopped or turned off the road.
As Wilson and Smith approached the area of sensor 317, they observed a pickup truck with overhead camper parked on the east side of the road facing south. The truck had Georgia license plates. Suspecting that this was the vehicle that had been traveling north from the border area, Officer Wilson felt the engine grill, and determined that the engine was warm, although the temperature was 22 °F. His suspicion confirmed, Wilson knocked on the camper door, announced he was a Border Patrol officer, and asked if anyone was inside.
After some delay Almand opened the door, stepped out with his hands up, and closed the camper door behind him. He had a black eye, a cut under one ear, and a bruise on one hand. Officer Wilson, in uniform, with his revolver in its holster, stood nearest to Almand. Officer Smith, also in uniform and carrying a shotgun, stood 10 to 15 feet behind Wilson and to his side. In spite of Almand’s assertion that Smith pointed the shotgun at him, the district court found that Smith kept it pointed toward the ground.
Officer Wilson identified himself as a Border Patrol officer and asked Almand his citizenship, place of birth, and where he had been. Almand replied that he was a U. S. citizen, born in Georgia, and that he had been traveling from Midland, Texas, south toward Big Bend National Park. In response to a question by Officer Smith, Al-mand claimed he had been parked at that *929spot for slightly over two hours. Considering the warmth of the engine and the sequential sensor readings indicating that Al-mand’s truck had been traveling north from the border, Officer Wilson testified that at this point he did not believe Almand was telling the truth. Officer Wilson asked if he was alone, and Almand answered affirmatively. Officer Wilson then asked Almand if he would mind Wilson looking inside the camper. According to Wilson’s testimony, Almand agreed. Almand claims that without saying anything, he reached into his pocket, removed the key, unlocked the camper door, and opened it. From outside, Wilson observed several gas cans in the camper and a large mound in the center aisle covered with a blanket. Wilson stepped inside the camper and found several large plastic bags under the blanket. After feeling the bags, Officer Wilson pierced the plastic revealing the presence of marijuana. He then stepped back outside the camper and arrested Almand.
II. THE STOP
The initial interrogation of Almand, to be legitimate, must be distinguished from the admittedly similar stop in United States v. Frisbie, 550 F.2d 335 (5th Cir. 1977).1 On oral argument the government conceded that Officer Wilson’s intrusion constituted a stop within the scope of Frisbie and United States v. Brignoni-Ponce, 422 U.S. 873, 95 S.Ct. 2574, 45 L.Ed.2d 607 (1975). That a stop under the Fourth Amendment “. . . does not mean a physical stop but rather a restraint of movement,” United States v. Robinson, 535 F.2d 881, 883 n.2 (5th Cir. 1976), is well settled. A stop occurred when Almand stepped out of the rear of the camper into the officers’ presence.
Although the officers in Frisbie relied on signals from some of the same sensor devices that traced Almand, different circumstances supported the officers’ decision to investigate in this case. The observations upon which the government sought to support the stop in Frisbie were made after the stop had begun. In that case Border Patrolman Nieto noticed that the truck was heavily loaded and that the driver was having difficulty stopping only as the truck was slowing down in response to his signal.
In the instant case Patrolman Wilson possessed considerable legitimately acquired information at the time he encountered Al-mand at the rear of the vehicle. In addition to sensor signals revealing the direction and sparse amount of traffic on Highway 385 at that time of day, Wilson knew that the vehicle he was investigating had stopped or turned off the highway. He was aware that sensor devices had indicated no southbound traffic along this stretch of Highway 385 that was not accounted for. After feeling the grill of the parked vehicle, Wilson was certain that it had only recently been parked. With these facts in mind, he asked Almand the standard questions relating to citizenship and his destination and point of departure. See Brignoni-Ponce, supra, 422 U.S. at 881-882, 95 S.Ct. at 2580, 45 L.Ed.2d at 616-617. Almand’s answers to these questions were inconsistent with the information that Wilson had gathered. Almand stated he had been parked two hours; Wilson knew the vehicle had recently been driven. Almand stated he was coming from Midland, Texas, by way of Marathon; Wilson knew that the vehicle had not come from that direction and was reasonably certain that it had come from the unpatrolled border area.2
*930Faced with responses that would necessarily arouse suspicion by their incongruity with the information he already possessed, Officer Wilson was authorized to investigate further. Brignoni-Ponce, supra, 422 U.S. at 881-882, 95 S.Ct. at 2580, 45 L.Ed.2d at 616; United States v. Worthington, 544 F.2d 1275, 1279-1280 (5th Cir. 1977). Nothing in Frisbie indicates that a law enforcement officer in these circumstances should curtail his inquiry.
III. THE SEARCH
For the search of the camper to be lawful, Almand’s consent must be shown, as no probable cause existed when Wilson asked Almand to open the camper door. Cf. United States v. McCann, 465 F.2d 147, 159 (5th Cir. 1972), cert. denied sub nom., Kelly v. United States, 412 U.S. 927, 93 S.Ct. 2747, 37 L.Ed.2d 154 (1973). The district court, faced with conflicting testimony on the consent issue, rejected Almand’s testimony where it diverged from the officers’, because Almand became nervous and his testimony lost spontaneity and was self-contradictory and inconsistent. The district court found that Officer Smith did not point his shotgun at Almand and that Officer Wilson did not say to him “We don’t like to shoot people.” While the testimony of officers Wilson and Smith was not exactly identical, the district court found that, in response to Wilson’s request to look inside the camper, Almand silently reached into his pocket, removed the key, and unlocked and opened the camper door. Based on these facts, the district court determined that consent was, in fact, freely and voluntarily given.
Almand testified that he did not know he had the right to refuse the officers’ request to search his camper. The district court deemed that fact immaterial. Under Schneckloth v. Bustamonte, 412 U.S. 218, 225, 93 S.Ct. 2041, 36 L.Ed.2d 854, 862 (1973), the absence of proof that the defendant knew he could withhold his consent, though a factor for consideration, is not of controlling significance in determining the voluntariness of consent. The district court found that the search of Al-mand’s camper was conducted pursuant to Almand’s voluntary waiver of his Fourth Amendment right. On the record before us, this decision must stand. See United States v. Watson, 423 U.S. 411, 424-425, 96 S.Ct. 820, 46 L.Ed.2d 598, 609-610 (1976).
Almand contends that Officer Wilson acted unreasonably in searching the covered plastic bags because they were not likely to contain illegal aliens. Courts have, for instance, suppressed the fruits of searches for aliens under automobile seats, United States v. Winer, 294 F.Supp. 731 (W.D.Tex.1969); in jacket pockets, Roa Rodriguez v. United States, 410 F.2d 1206 (10th Cir. 1969); and between the trunk panel and inside wall of an automobile, Valenzuela-Garcia v. United States, 425 F.2d 1170 (9th Cir. 1970). In the circumstances of this case, however, Officer Wilson acted reasonably in investigating further the 550 pound mass occupying the center of the floor of Almand’s camper truck. He felt the contents of the bags before he opened them and suggested that he concluded that they did contain contraband. The officer had many years of experience as a Border Patrol officer.
Judgment AFFIRMED.