delivered the opinion of the court:
On the evening of February 23, 1975, the defendant, *289Richard Eugene Blitz, was stopped by sheriff’s officers of Randolph County while driving his car in Steeleville. A search of the trunk revealed cannabis, and the defendant was charged with its possession (Ill. Rev. Stat. 1973, ch. 56½, par. 704(d)). He moved to suppress the cannabis, and the trial court allowed the motion, holding that the searching officer lacked probable cause to open and search the trunk of the car. The State appealed and the appellate court, with one judge dissenting, affirmed the suppression of the evidence (38 Ill. App. 3d 419). We allowed the State’s petition for leave to appeal.
Kenneth Beam, a deputy sheriff of Randolph County, testified at the hearing on the motion to suppress that some officer of his office had received a tip from a “reliable informer” that drugs were being sold in a house in Percy occupied by George Kraft. Acting on this tip the sheriff’s office maintained surveillance on the house for about a week prior to February 23, 1975. He said that, on the evening of February 23, he had the Kraft house under surveillance from a distance of a block and a half and that in a 15- to 20-minute period he observed between four to six cars separately pull up to the house. He testified that in each instance a person left the car, entered the house and returned to the car 5 to 10 minutes later. The auto would then be driven away. At about 7:30 p.m. he observed a car driven by the defendant park outside the Kraft house. Two persons left the car, entered the house and returned carrying a brown bag which was placed in the trunk. He said the bag was of a type large enough to carry 16 to 25 pounds of food. The defendant later testified that he did carry a brown paper grocery bag from the house but stated he placed it in the rear seat of the auto, not in the trunk.
Beam stated that he followed the defendant’s car when it left the house and that it headed in the direction of Steeleville. He said that while following the car he tried to read the number on the rear license plate but he could. *290not do so because the license plate light was out and in addition because a trailer hitch on the car obstructed his view of the plate. He testified that he radioed for backup assistance because there were a number of persons in the car and that as he would radio he would notice the occupants looking back at him. He concluded from this, he said, that the occupants of the defendant’s car were monitoring his radio calls. He said he decided to stop the car in Steeleville because it was a well-lighted area and because he wanted to give his backup officers ample time to come to assist him.
He testified that when he stopped the car the defendant “jumped out of the car and ran back [toward him], acting in a nervous manner.” He said he told the defendant that he had stopped him because of the license plate violation and • that he asked for and was given what apparently was a valid driver’s license. He said that as he walked toward the defendant’s car he heard what he thought may have been police transmissions coming from an eight-band radio in the defendant’s car. The witness stated that when he saw Michael Blitz, the defendant’s brother, turn a knob on the radio, he opened the car door and took the radio from Michael. He then ordered the occupants out of the car and told the four of them and the defendant to place their hands on the trunk of the car. He said he kept a shotgun trained on the occupants for his own protection until the other officers arrived. When they did, the occupants were searched. A hunting knife was found on Michael Blitz, and he was then placed under arrest for possession of the knife, and Richard Blitz was arrested for the license plate light violation. He stated that the defendant gave him permission to search the interior of the car and then the trunk. (The appellate court held that there was not a valid consenT to search the trunk. Whether there was a consent is not an issue here, because the People rely on other grounds to justify the search.) There was *291cannabis in the trunk.
On cross-examination Officer Beam stated he had stopped the car because of the license plate light violation and because he “wanted to look into that car *** to see if there was cannabis in there.” He said that he believed the car contained drugs and that there was cannabis in the bag because of all of the activities he saw while he had the Kraft house under surveillance, because the two occupants of the defendant’s car placed the bag in the trunk and because his office had “a report from a reliable source, there was drugs being sold out of the house.” He said he did not remember who in the sheriff’s office had told him of the tip or the circumstances of its being given.
When asked: “At the time you stopped the vehicle the only violation that you were aware of was of the traffic violation?” the officer responded: “No, I believed they had cannabis in it.” Later he was asked: “And you wanted to look into that car when you stopped that car to see if there was cannabis in there?” He answered yes. He also testified that he had followed the defendant’s car from Percy and had stopped it so that he could examine the trunk.
The question presented to us is whether there was probable cause to justify the search of the trunk of the defendant’s car. What this court observed in People v. Watkins (1960), 19 Ill. 2d 11, 18-19, is relevant:
“The constitution prohibits only unreasonable searches; it permits those that are reasonable. The critical issue in each case must be whether the situation that confronted the officer justified the search. That question can not be determined by an indiscriminate application of legal concepts that were evolved to meet quite different problems. ***
*** Police officers often must act upon a *292quick appraisal of the data before them, and the reasonableness of their conduct must be judged on the basis of their responsibility to prevent crime and to catch criminals.”
In determining whether there was probable cause we must look at all of the circumstances presented to the investigating officer. Probable cause exists when “the facts and circumstances within the arresting officer’s knowledge are sufficient to warrant a man of reasonable caution in believing that an offense has been committed and that the person arrested has committed the offense. [Citation.] ” (People v. Robinson (1976), 62 Ill. 2d 273, 276.) Facts sufficient to establish probable cause need not be sufficient to establish guilt beyond a reasonable doubt (Draper v. United States (1969), 358 U.S. 307, 311-12, 3 L. Ed. 2d 327, 331, 79 S. Ct. 329), and probable cause may be founded upon evidence which would not be admissible at trial (People v. Jones (1964), 31 Ill. 2d 42, 47). The court in United States v. Davis (D.C. Cir. 1972), 458 F.2d 819, 821, commented broadly on probable cause:
“Probable cause does not emanate from an antiseptic courtroom, a sterile library or a sacrosanct adytum, nor is it a pristine ‘philosophical concept existing in a vacuum,’ Bell v. United States, 102 U.S. App. D.C. 383, 386, 254 F.2d 82, 85 (1958), but rather it requires a pragmatic analysis of ‘everyday life on which reasonable and prudent men, not legal technicians, act.’ Brinegar v. United States, 338 U.S. 160, 175, 69 S. Ct. 1302, 1310, 93 L. Ed. 1879 (1949). It is to be viewed from the vantage point of a prudent, reasonable, cautious police officer on the scene at the time of the arrest guided by his experience *293and training. Jackson v. United States, 112 U.S. App. D.C. 260, 302 F.2d 194 (1962). It is ‘a plastic concept whose existence depends on the facts and circumstances of the particular case.’ Bailey v. United States, 128 U.S. App. D.C. 354, 357, 389 F.2d 305, 308 (1967). See McCray v. Illinois, 386 U.S. 300, 304, 87 S. Ct. 1056, 18 L. Ed. 2d 62 (1967); Beck v. Ohio, supra, 379 U.S. at 91, 85 S. Ct. 223; Brinegar v. United States, supra, 338 U.S. at 175-176, 69 S. Ct. 1302. Because of the kaleidoscopic myriad that goes into the probable cause mix ‘seldom does a decision in one case handily dispose of the next.’ Hinton v. United States, 137 U.S. App. D.C. 388, 391, 424 F.2d 876, 879 (1969). It is however the totality of these facts and circumstances which is the relevant consideration. Davis v. United States, 133 U.S. App. D.C. 172, 173, 409 F.2d 458, 459 (1969); Dixon v. United States, Ill U.S. App. D.C. 305, 306, 296 F.2d 427, 428 (1961). Viewed singly these factors may not be dispositive, yet when viewed in unison the puzzle may fit.”
The deputy sheriff, Beam, testified that deputifes of his office had kept the Kraft house under surveillance for a week prior to February 23, 1975, because of the tip that drugs were being sold there. (There was no attempt by the defendant to controvert this through the subpoenaing of patrol records of the sheriff’s office or through the testimony of other deputies.) Beam personally observed four to six cars separately arrive at the house in a 15- to 20-minute period. In each instance people left their cars, entered the house and returned shortly to their cars. He testified he saw the defendant park his car outside the *294house and that two persons left the auto and entered the house. They returned to the car within 10 minutes and the witness said he saw these two open the trunk and place a brown paper bag in it. Considering the totality of the circumstances we judge that Beam had probable cause to search the defendant’s trunk. This probable cause was not destroyed or diminished by Beam’s later observing the absence of a license plate light on the car. In People v. Brown (1967), 38 Ill. 2d 353, 358, this court, in holding reasonable the search of an automobile trunk, observed: “It is the duty of police officers when confronted with circumstances giving an appearance of criminal activity to investigate in an effort to determine whether such criminal activity, in fact, exists.” Under the circumstances Beam would have been subject to criticism had he not attempted to ascertain whether the defendant’s car did in fact contain drugs.
For the reasons given, the judgments of the circuit and appellate courts are reversed, and the cause is remanded to the circuit court of Randolph County for further proceedings.
Reversed and remanded.