Appellee, Jack Manuel Alvarez, was indicted in a three-count indictment charging him with possession with intent to distribute cocaine (21 U.S.C. § 841(a)(1)), possession of an unregistered firearm (26 U.S.C. § 5861(d)), and possession of a firearm with the serial number removed (26 U.S.C. § 5861(h)). Appellant contends that the district court erred in suppressing evidence seized after a stop of Alvarez’ automobile.
Background
On May 12, 1988, at approximately 10:28 am, an unidentified male caller telephoned the Santa Ana Police Department with information of a possible bank robbery that was to take place that morning. The caller refused to identify himself but claimed that the robbery was going to happen “in about 10 minutes at the Bank of America on Eighth and Main. The man is driving a white Mustang GT and he’s got explosives with him.” The caller described the man in the car as “tall, dark, looks kinda Mexican and he’s probably in the back of the bank.” When asked how he knew what was going to happen, the caller stated, “I know it’s going to happen. Just believe me, he’s there.”
Based on this information, several patrol cars were dispatched to the bank. Officers observed a white Mustang GT backed into a parking space facing the bank with a Hispanic looking male occupant. The officers observed the car for about five minutes. According to the government, “[a]s other police officers arrived at the bank, one of the police cars drove past the bank, within Alvarez’ field of vision,” after which the white Mustang GT left the parking lot. The police followed the car for a short distance and then pulled it over. One of the officers, using his public address system, ordered the suspect not to move and to keep his hands in plain view. Three officers approached Alvarez with their weapons drawn, and ordered him out of the car. Alvarez complied with all of the officer’s instructions. While placing Alvarez' arm behind his back, one of the officers observed a bulge underneath Alvarez’ jacket and removed a loaded nine millimeter pistol from the suspect’s right side. Alvarez was handcuffed and a pat down search revealed another loaded nine millimeter pistol and two ammunition clips. The police then searched the trunk of the car and found a partially assembled belt-feed M-6 machine gun, a M-16 fully automatic rifle, ammunition for both of these weapons, and a substantial quantity of cocaine.
At the hearing on the motion to suppress the evidence found in the trunk, the anonymous caller was identified as Michael Soler, a personal acquaintance of Alvarez. At the time Soler made the call he was on bail awaiting trial in San Bernardino on charges of the sale and transportation of cocaine. Soler, at the hearing testified he had spent the morning with Alvarez on the day Alvarez was arrested. Soler testified he was going shopping at South Coast Plaza that day, but that, although out of his way, he followed Alvarez to the bank. When Alvarez turned into the bank, Soler went directly to a phone booth and called the police. Soler also testified that he was not working for the police officer when he made the call. The district court ruled that Alvarez had not met his burden of proof that Soler was acting at the behest of the government *836and that the motion to suppress could not be granted on that ground.1 694 F.Supp. 734.
In granting Alvarez’ motion, the district court concluded that it did not need to address the issue of whether the stop was an arrest because under either a test of probable cause or reasonable suspicion the stop was unlawful.2 The government appeals, and we now reverse.
Standard of Review
Whether there was sufficient founded suspicion to justify an investigatory stop is a mixed question of law and fact that requires a de novo review. See United States v. Thomas, 863 F.2d 622, 625 (9th Cir.1988) (Thomas). Whether an arrest has occurred depends on all the surrounding circumstances and whether, under all the circumstances, “a reasonable person would conclude he was under arrest.” United States v. Patterson, 648 F.2d 625, 632 (9th Cir.1981) (internal citations omitted); see also, United States v. Buffington, 815 F.2d 1292, 1300 (9th Cir.1987) (Buffington). Whether a search was lawful presents a mixed question of law and fact re viewable de novo. United States v. Linn, 862 F.2d 735, 739-40 (9th Cir.1988); see also, United States v. McConney, 728 F.2d 1195, 1204-05 (9th Cir.1984), cert. denied, 469 U.S. 824, 105 S.Ct. 101, 83 L.Ed.2d 46 (1984).
Discussion
A. Validity of the Investigatory Stop
The government’s first challenge to the district court’s ruling to suppress the evidence is that the initial detention of Alvarez’ vehicle was legal. Specifically, the government maintains that the officers’ detention of Alvarez was based upon a reasonable articulable suspicion of illegal activity.
In order to justify an investigatory stop there must be “some objective manifestation that the person stopped is, or is about to be, engaged in criminal activity.” United States v. Cortez, 449 U.S. 411, 417, 101 S.Ct. 690, 695, 66 L.Ed.2d 621 (1981); Terry v. Ohio, 392 U.S. 1, 88 S.Ct. 1868, 20 L.Ed.2d 889 (1968); Thomas, 863 F.2d at 625. The stop is evaluated by looking at the “totality of the circumstances” and then determining, based upon the whole picture, whether the detaining officers had a particularized objective basis for suspecting the particular person of criminal activity. Cortez, 449 U.S. at 417-18, 101 S.Ct. at 694-95.
The question here is whether the anonymous tip was sufficiently corroborated by police observations to provide the officers with reasonable suspicion to warrant an investigatory stop. We assume *837that the tipster was not working with law enforcement officers to create the appearance of reasonable suspicion by which the stop and subsequent search might be justified.3
In Illinois v. Gates, 462 U.S. 213, 103 S.Ct. 2317, 76 L.Ed.2d 527 (1983), the Supreme Court, in deciding the weight of an anonymous informant’s tip, applied a “totality-of-the-eircumstances” analysis, requiring a balance assessment of the relative weight of all the “indicia of reliability.” Gates, 462 U.S. at 235, 103 S.Ct. at 2330-31. In Gates, the details of an anonymous informant’s letter were corroborated by police observation. The Supreme Court reasoned that the inherently suspect nature of an anonymous tip was diminished by independent corroboration by police of the letter’s predictions of future activities of the suspect. Gates, 462 U.S. at 244-45, 103 S.Ct. at 2335-36.
The D.C. Circuit has held that an anonymous tip can provide sufficient reasonable suspicion when the tip “was corroborated in every significant detail by [the police officer’s] pre-stop surveillance.” United States v. McClinnhan, 660 F.2d 500, 502 (D.C.Cir.1981) ) (McClinnhan); see also United States v. White, 648 F.2d 29 (D.C. Cir.), cert. denied, 454 U.S. 924, 102 S.Ct. 424, 70 L.Ed.2d 233, 235 (1981).
In McClinnhan, the police were given a detailed description of the suspect and told that he had a sawed-off shotgun in a brief case. The police spotted a man fitting the description standing with a brief case. The police approached the man and initiated an investigatory detention and weapons frisk. They also conducted a warrantless search of the brief case which was next to the man.
The court noted “that it is possible for anyone with a grudge to fabricate a tip whose neutral details, such as clothing or location, would provide the [necessary] corroboration ... for a stop.” McClinnhan, 660 F.2d at 503. Nonetheless, the court held that the officers’ suspicions about the suspect, based on an anonymous tip that, while lacking facial indicia of reliability, was corroborated in every significant detail by the officers’ pre-stop surveillance, justified an investigative detention of the suspect.
Reviewing the facts and surrounding circumstances of this case from the perspective of an experienced law officer, we conclude that the initial warrantless stop was proper because the officers had a reasonable suspicion that Alvarez was involved in criminal conduct. See Thomas, 863 F.2d at 626-27; United States v. Sutton, 794 F.2d 1415, 1426 (9th Cir.1986) (Sutton). Here, the officers, through an anonymous tip, were informed that a “tall, dark, [male who] looks kinda Mexican” in a “White Mustang GT” was parked in back of the bank and was going to rob the bank. The police were also informed that the man had explosives. The police officers observed Alvarez sitting in a vehicle which fit the description given by the anonymous tipster. The vehicle was parked in the bank’s parking lot and was unusually positioned — front end facing outward. The first police officer to arrive on the scene observed the car and its occupant for approximately five minutes; two other marked police units appeared on the scene. The appellant did not depart from the bank until one of these two marked police cars drove within the appellee’s line of sight.
“When law enforcement officials corroborate the details of an anonymous informant’s tip, the tip can give rise to a reasonable articulable suspicion.” United States v. Rodriguez, 835 F.2d 1090, 1092 (5th Cir. 1988) {Rodriguez — Fifth Circuit). Here, the officers verified each of the details of the tip. These facts were consistent with the actions of a would-be bank robber who decided to take a break until the coast was clear. The anonymous tip, corroboration of the details of the tip, and the pre-stop observations of the police officers gave rise to reasonable articulable suspicion to make an investigatory stop. The “Fourth Amendment does not, particularly where the reported contraband [is explosives], re*838quire a police officer to ignore his well-founded doubts and accordingly will permit an investigative detention.” 660 F.2d at 503.
Alvarez argues that the activities observed by the police officers are innocent and not probative of criminal activity. “Taken alone he might be correct. But when viewed in light of the tip and other circumstances noted above, this same activity appears highly suspicious. It is not uncommon for seemingly innocent conduct to provide the basis for [reasonable suspicion].” United States v. Rodriguez, 869 F.2d 479, 483 (9th Cir.1989) (Rodriguez— Ninth Circuit) (citing Gates, 462 U.S. at 244 n. 13, 103 S.Ct. at 2335 n. 13); see also Sutton, 794 F.2d at 1427. The fact that the officers “did not actually observe any criminal activity is irrelevant,” as is the fact that Alvarez could have been at the bank for innocent purposes. Sutton, 794 F.2d at 1427. We hold that under the circumstances of this ease the officers had a particularized and objective basis for making the investigatory stop of Alvarez’ vehicle.
B. Validity of the Manner of the Investigatory Stop
After stopping the vehicle, one of the police officers immediately ordered Alvarez not to move and to keep his hands in view. The officers then approached the vehicle with their weapons drawn and ordered Alvarez to step out of the vehicle. Appellant argues that the investigatory stop escalated to a full arrest when he was forced to exit his car at gunpoint necessitating a showing of probable cause.
The Supreme Court has permitted limited intrusions on a suspect’s liberty during a Terry stop to protect the officer’s safety; a police officer may take reasonable measures to neutralize the risk of physical harm and to determine whether the person in question is armed. United States v. Hensley, 469 U.S. 221, 235, 105 S.Ct. 675, 683-84, 83 L.Ed.2d 604 (1985); Terry, 392 U.S. at 24, 88 S.Ct. at 1881-82. In this circuit it has been held that “[t]he use of force does not convert the [investigatory] stop into an arrest if it occurs under circumstances justifying fears of personal safety.” Buffington, 815 F.2d at 1300 (Terry stop where police officers forced suspects to exit car and lie down on pavement at gunpoint); accord United States v. Parr, 843 F.2d 1228 (9th Cir.1988) (briefly placing suspect in police car does not convert a Terry stop into an arrest requiring probable cause). See United States v. Greene, 783 F.2d 1364, 1367-68 (9th Cir.), cert. denied, 476 U.S. 1185, 106 S.Ct. 2923, 91 L.Ed.2d 551 (1986) {Greene) (investigatory stop where officers instructed suspects to put their hands on the car and then drew their weapons); United States v. Taylor, 716 F.2d 701, 708 (9th Cir.1983) {Taylor) (investigatory stop where officers approached suspects with their weapons drawn after having been warned that the suspects were dangerous).
In this case, the totality of the circumstances indicate that the police conducted an investigatory stop rather than an arrest without probable cause. The police, through their independent observations, verified the details of the anonymous tip. After corroborating the details of the tip, including the suspect’s location, description and vehicle, the police officers had additional reason to credit the portion of the tip that indicated the suspect was carrying explosives. “Although approaching a suspect with dfawn weapons are extraordinary measures, such police procedures [are] justified ... as a reasonable means of neutralizing danger to police and innocent bystanders.” United States v. Taylor, 857 F.2d 210, 214 (5th Cir.1988); United States v. Serna-Barreto, 842 F.2d 965, 968 (7th Cir.1988) {Terry stop does not turn into an arrest as soon as an officer points his gun at the suspect); Taylor, 716 F.2d at 708. In Taylor, the officers had been warned that the suspects were dangerous and approached the suspects’ vehicle with weapons drawn. We held that “[w]hen the officers stopped [the suspects] to question them ... the officers were justified in drawing their weapons in self protection,” and the officers’ drawn weapons did not convert the Terry stop into an arrest. Taylor, 716 F.2d at 708-09.
*839Contrary to appellee’s contentions, United States v. Strickler, 490 F.2d 378 (9th Cir.1974), does not require a different result. In that case, we held that an armed approach to a surrounded vehicle was an arrest. In Strickler, “it is clear that ... the police had no legitimate fear for their safety and only tenuous reasons to believe that the occupants of the car were involved in the drug transaction.” Taylor, 716 F.2d at 708-09. In the present case, the police officers had strong reason to believe that Alvarez was armed with explosives and legitimate reasons to fear for their safety. We hold that the manner of the stop did not convert the investigatory stop into an arrest.
C. Validity of the Frisk
The decision to frisk Alvarez for weapons was similarly justified. “Police are entitled to take steps to assure that the person stopped is not armed.” Greene, 783 F.2d at 1368. “The purpose of the Terry frisk is ‘to allow the officer to pursue his investigation without fear of violence.’ ” United States v. Bautista, 684 F.2d 1286, 1289 (9th Cir.1982), cert. denied, 459 U.S. 1211, 103 S.Ct. 1206, 75 L.Ed.2d 447 (1983) (quoting Adams v. Williams, 407 U.S. 143, 146, 92 S.Ct. 1921, 1923, 32 L.Ed.2d 612 (1972)). In this case, the corroborated details of the anonymous tip noted by the officers allowed them to form the reasonable suspicion that Alvarez was armed with explosives. Additionally, when the officers placed Alvarez’ arm behind his back they observed a large bulge underneath his jacket. The visible bulge was a significant factor in clueing in the officers to Alvarez’ possession of a gun. It was thus reasonable for the officers to take the precautionary step of a pat frisk to insure that Alvarez was not armed. We conclude that the officers acted properly in frisking Alvarez.
D. Validity of the Search of the Vehicle
The next question is whether the officers’ warrantless search of Alvarez’ automobile including the trunk was proper. Due to an automobile’s mobility, a search warrant does not need to be obtained prior to a search of the automobile. However, the search must still be supported by probable cause. California v. Carney, 471 U.S. 386, 394-95, 105 S.Ct. 2066, 2070-71, 85 L.Ed.2d 406 (1985); United States v. Miller, 812 F.2d 1206, 1208 (9th Cir.1987). Officers who have probable cause to believe that an automobile contains evidence of a crime may search the vehicle, including the trunk and all containers in which there is probable cause to believe that evidence was concealed. United States v. Ross, 456 U.S. 798, 102 S.Ct. 2157, 72 L.Ed.2d 572 (1982). Probable cause exists if, under the totality of the circumstances, “there is a fair probability that contraband or evidence of a crime will be found in a particular place.” Rodriguez-Ninth Circuit, 869 F.2d at 484.
In this case probable cause existed to search the vehicle. The pat frisk revealed two loaded nine millimeter pistols inside the appellee’s waistband. The moment the police discovered the two concealed weapons, they had reason to believe that Alvarez was involved in the criminal activity described by the tipster and they were provided with additional reason to suspect that Alvarez possessed explosives. The verified details of the anonymous tip “coupled with [the officers’] experience gave rise to probable cause to believe the car and trunk contained contraband.” Rodriguez—Fifth Circuit, 835 F.2d at 1093.
In the officers’ search of the car, two large black bags and a long beige box were found inside the trunk. These containers could easily conceal explosives; additionally, the officers observed a barrel of a rifle protruding from one of the bags. These circumstances justify the officers’ search of the bags and box in the trunk.
Conclusion
Accordingly, we reverse the district court’s decision to suppress the evidence found in the trunk. The case is remanded for further proceedings consistent with this opinion.
REVERSED AND REMANDED.
. The district court was troubled by evidence that Soler was working with law enforcement officers to create the appearance of reasonable suspicion to justify the initial stop and subsequent seizure. The court noted that evidence suggested that Modesto Perales, an ex-police officer, may have been the source of cocaine for both Soler and Alvarez. Further, the court noted that its own docket contained a three-count indictment against Perales for possession with an intent to distribute and distribution of cocaine. The court stated that, if in fact, in cooperation with the United States, Soler had induced Alvarez to go and wait at the bank with cocaine and weapons, and then made the "anonymous” telephone call, a motion to suppress would have been granted; if it were not necessary to suppress the evidence on other grounds, the district court concluded that it would be inclined at least to invite more evidence on the question.
. "A gunpoint stop cannot be justified on the basis of anonymous and unidentified bald accusations, where nothing else the police observe gives any reason to believe a crime is being, has been or is about to be committed. In such circumstances, there can be neither probable cause nor reasonable suspicion which would justify the gunpoint stop and search.
The importance of this issue should not be minimized. The more broadly the law construes the duty of police officers to investigate suspicious circumstances and their right to do so with drawn weapons, the more likely it becomes that innocent persons will die or be seriously injured. Anytime two people confront each other with weapons drawn, there is a great risk that one or both will shoot. Because the likelihood of tragedy is so high when armed confrontations become necessary, it is of the utmost social importance to clearly and narrowly define the occasions which call for such highly volatile confrontations.”
District Court's Memorandum and Order granting defendant’s motion to suppress at 8-9.
. At oral argument, the appellee’s counsel stated that he did not want us to address the issue of the tipster being associated with the government.