*478 In this interlocutory appeal by the Commonwealth, we must decide whether the *1232 information provided by a first-time, confidential police informant (CI) was sufficiently corroborated by a single, imperfectly executed controlled "buy" of cocaine for the purposes of establishing probable cause for the issuance of a warrant to search the defendant's apartment. We conclude that the affidavit was sufficient to establish the CI's basis of knowledge and veracity, and that the information provided by the CI, along *479 with information gathered by the police, as set forth in the affidavit in support of the search warrant, established probable cause. Accordingly, we reverse the order allowing the defendant's motion to suppress.

Background . The affidavit filed as part of the warrant application contained the following facts.

In November, 2015, Detective Gracia of the New Bedford police department spoke with the CI, whose identity and whereabouts were known to the police. 1 The CI stated that they had contacted the defendant, Paulo Monteiro, by telephone or had "show[n] up [at] his residence" in New Bedford to purchase cocaine in the past. The CI informed Detective Gracia that they continue to purchase cocaine from the defendant. The CI provided Detective Gracia with a physical description of the seller ("a Cape Verdean male 20 years old approx 6' tall with a medium build") and the seller's address. Detective Gracia confirmed via the police department's computer system that a person named Paulo Monteiro had the same listed address as that provided by the CI. Detective Gracia also reviewed the defendant's criminal record and determined that he was on probation for statutory rape. A booking photograph of the defendant was shown to the CI. The CI stated that the person in the photograph, whom the CI identified as the defendant, was the person who had sold cocaine to the CI in the past.

Detective Gracia later met the CI to arrange a controlled buy of cocaine from the defendant. The CI was searched and determined to be free of contraband and money. Detective Gracia then gave the CI money to purchase cocaine from the defendant. Detective Gracia and other members of the New Bedford police department maintained surveillance of the CI. They observed the CI walking toward the rear exterior door of the defendant's apartment building. 2 A short time later, the CI was seen leaving the walkway leading to the rear exterior door. The defendant was not observed entering or exiting the apartment building through the rear exterior *480 door. The CI was kept under surveillance until the CI met Detective Gracia at a predetermined location where the CI provided Detective Gracia with a quantity of what the CI said was cocaine. The CI stated that they purchased the cocaine from the defendant inside his first-floor apartment. The CI was again searched and determined to be free of money and contraband. The material the CI turned over to the police was field tested and found to be cocaine.

Detective Gracia applied for, and a magistrate subsequently issued, a warrant to search the defendant's apartment. Upon execution of the search warrant, the police *1233 found narcotics and drug paraphernalia inside the defendant's apartment. An indictment was returned against the defendant for trafficking in cocaine. See G. L. c. 94C, § 32E( b ). The defendant moved to suppress the contraband and related drug paraphernalia found during the search on the basis that the affidavit provided to the magistrate did not establish probable cause. The defendant's motion to suppress was allowed after the motion judge concluded that the affidavit failed to establish both the CI's basis of knowledge and veracity. For the reasons set forth below, we reverse.

Discussion . Article 14 of the Massachusetts Declaration of Rights requires that a search warrant issue only upon a showing of probable cause. Commonwealth v. Foster , 471 Mass. 236 , 241, 28 N.E.3d 427 (2015). In determining whether the probable cause standard was met, our inquiry "begins and ends with the 'four corners of the affidavit' " supporting the application for the search warrant. Commonwealth v. O'Day , 440 Mass. 296 , 297, 798 N.E.2d 275 (2003), quoting from Commonwealth v. Villella , 39 Mass. App. Ct. 426 , 428, 657 N.E.2d 237 (1995). "Because a determination of probable cause is a conclusion of law, we review a search warrant affidavit de novo." Foster , supra at 242, 28 N.E.3d 427 .

In Commonwealth v. Upton , 394 Mass. 363 , 373, 476 N.E.2d 548 (1985) ( Upton II ), the Supreme Judicial Court determined that "art. 14 provides more substantive protection to criminal defendants than does the Fourth Amendment" to the United States Constitution. When an affidavit in support of a search warrant is based on information supplied by an unknown informant, art. 14 requires the magistrate called upon to issue a search warrant to apply the so-called Aguilar - Spinelli test to assess whether the affidavit is sufficient to establish probable cause to issue the warrant. See Aguilar v. Texas , 378 U.S. 108 , 84 S.Ct. 1509 , 12 L.Ed.2d 723 (1964) ;

*481 Spinelli v. United States , 393 U.S. 410 , 89 S.Ct. 584 , 21 L.Ed.2d 637 (1969). 3

"Where information from an unidentified informant is relied on to supply probable cause to search, art. 14 ... requires that the affidavit apprise the magistrate of (1) some of the underlying circumstances from which the informant concluded that contraband was where he claimed it was (the basis of knowledge test), and (2) some of the underlying circumstances from which the affiant concluded that the informant was credible or the information reliable (the veracity test)."

Commonwealth v. Warren , 418 Mass. 86 , 88, 635 N.E.2d 240 (1994).

*1234 The defendant concedes, and we agree, that the basis of knowledge test was satisfied by the CI's statement that they had purchased cocaine from the defendant inside the target apartment within seventy-two hours of the warrant issuing. See Commonwealth v. Desper , 419 Mass. 163 , 166, 643 N.E.2d 1008 (1994).

We next examine whether the veracity prong has been satisfied. The affidavit submitted to the magistrate indicated that the CI was a first-time, confidential police informant, which rendered the statements made by the CI contained in the affidavit, standing alone, insufficient to satisfy the veracity prong of the Aguilar - Spinelli test. See Commonwealth v. Alfonso A ., 438 Mass. 372 , 376, 780 N.E.2d 1244 (2003) ("Although police knowledge of the CI's 'identity' and 'whereabouts' would not be adequate standing alone to confirm the informant's reliability, it is a factor that weighs in *482 favor of reliability"); Commonwealth v. Figueroa , 74 Mass. App. Ct. 784 , 787, 911 N.E.2d 206 (2009) (information from first-time informant "ordinarily would not meet the veracity requirements imposed by art. 14").

However, "a properly monitored controlled purchase of illegal drugs provides sufficient corroborating evidence to overcome any shortfalls in meeting the constitutional reliability requirements imposed on confidential informants." Figueroa , supra at 787-788, 911 N.E.2d 206 . See Commonwealth v. Luna , 410 Mass. 131 , 134, 571 N.E.2d 603 (1991) (two controlled purchases of narcotics by confidential informant were sufficient, standing alone, to provide probable cause to search defendant's home); Warren , 418 Mass. at 87, 89 , 635 N.E.2d 240 (tip containing detailed information about defendant's apartment and location of drugs contained therein, coupled with single controlled buy, sufficient to establish informant's veracity); Villella , 39 Mass. App. Ct. at 427-428 , 657 N.E.2d 237 (probable cause established where police corroborated portions of informant's detailed tip and informant made single controlled buy at defendant's residence through intermediary). See also Commonwealth v. Cruz , 430 Mass. 838 , 842 n.2, 724 N.E.2d 683 (2000), citing Warren , supra . 4 In Desper , 419 Mass. at 168 , 643 N.E.2d 1008 , the Supreme Judicial Court set forth the essential components of a controlled buy:

"(1) a police officer meets the informant at a location other than the location where is it suspected that criminal activity is occurring; (2) the officer searches the informant to ensure the informant has no drugs on his person and (usually) furnishes the informant with money to purchase drugs; (3) the officer escorts or follows the informant to the premises where it is alleged illegal activity is occurring and watches the informant enter and leave those premises; and (4) the informant turns over to the officer the substance the informant has purchased from the residents of the premises under surveillance."

Here, the affidavit does not indicate that the affiant observed the CI's physical entry into, or exit from, the building housing the *483 defendant's apartment during the course of the controlled buy. 5 The defendant *1235 argues that this deficiency in the controlled buy rendered the information provided by the CI unreliable for the purposes of establishing probable cause.

Although "the steps customary in a controlled buy should be taken" when a controlled buy is being used to corroborate a statement made by a confidential informant that otherwise would not be sufficient to establish probable cause, id . at 170, 643 N.E.2d 1008 , probable cause may nevertheless be established where the police fail to comply with one of the four investigatory steps customarily associated with a controlled buy. 6 See id . at 170-171, 643 N.E.2d 1008 (probable cause requirement was met where police failed to search confidential informant for contraband before two controlled buys). Here, the magistrate was not compelled to conclude that because the police did not observe the CI's physical entry into and exit from the apartment building, the information contained in the affidavit was insufficient to establish probable cause. In the circumstances of this case, the police observation of the CI walking toward the door to the building and then a few minutes later walking away from that area and turning over a quantity of drugs, when coupled with the other facts, was sufficient to support the magistrate's conclusion that the CI was credible. In cases involving a controlled buy of drugs from a seller who is located inside a multiunit building, we do not require that the police observe the informant enter the particular apartment where the transaction is reported to have occurred in order to demonstrate the reliability of the informant. See Warren , 418 Mass. at 90 , 635 N.E.2d 240 ("It is not fatal to the warrant application that the police did not observe which of the three apartments the informant entered. Based on the information provided by the informant and their own observations, the police could infer that the defendant was dealing drugs from his second-floor apartment").

"In dealing with probable cause ... we deal with probabilities. These are not technical; they are factual and practical considerations *484 of everyday life on which reasonable and prudent men ... act." Commonwealth v. Hason , 387 Mass. 169 , 174, 439 N.E.2d 251 (1982), quoting from Brinegar v. United States , 338 U.S. 160 , 175, 69 S.Ct. 1302 , 93 L.Ed. 1879 (1949). To that end, "the question is whether reasonable and prudent people would act on the basis of the information gathered by the police, not whether the information would satisfy legal technicians." Commonwealth v. Fontaine , 84 Mass. App. Ct. 699 , 704, 3 N.E.3d 82 (2014), citing Brinegar , supra . Here, the controlled buy was executed less than seventy-two hours before the filing of the warrant application and affidavit. The affidavit indicated that the CI, whose identity and whereabouts were known to Detective Gracia, see Alfonso A ., 438 Mass. at 375-376 , 780 N.E.2d 1244 , positively identified the defendant as having sold the CI cocaine from the target apartment in the past. The CI reported that they had been buying cocaine from the defendant at the location to be searched. The affidavit further stated that the defendant was on probation for committing a serious felony. The affidavit indicated *1236 that all the essential steps of a controlled buy were met, with the exception that the CI was not directly observed entering or exiting the building or target apartment. While the execution of the controlled buy was lacking in this respect, the affidavit stated that the CI was observed walking toward the rear door of the defendant's apartment building, returned a short time later under police surveillance with a quantity of cocaine from the vicinity of the rear exterior door, and informed the officers that they purchased the cocaine from the defendant inside the apartment. This information was sufficient to allow the magistrate to reasonably infer that the CI entered and purchased drugs in the defendant's apartment. See Warren , 418 Mass. at 90 , 635 N.E.2d 240 ; Fontaine , supra at 704, 3 N.E.3d 82 , quoting from Commonwealth v. Jimenez , 438 Mass. 213 , 218, 780 N.E.2d 2 (2002) ("In reviewing affidavits in support of search warrants, we allow 'considerable latitude' for the drawing of inferences"). 7 *485 Finally, we are mindful that in order to encourage the police to apply for search warrants, a reviewing court should allow "a certain leeway or leniency in the after-the-fact review of the sufficiency of applications for warrants." Commonwealth v. Corradino , 368 Mass. 411 , 416, 332 N.E.2d 907 (1975). See United States v. Ventresca , 380 U.S. 102 , 109, 85 S.Ct. 741 , 13 L.Ed.2d 684 (1965) ; Commonwealth v. Cruz , 430 Mass. 838 , 840, 724 N.E.2d 683 (2000) ; Commonwealth v. Monterosso , 33 Mass. App. Ct. 765 , 770, 604 N.E.2d 1338 (1992).

For the above reasons, we conclude that the affidavit, "taken as a whole and read in a commonsense fashion," Alfonso A ., 438 Mass. at 375 , 780 N.E.2d 1244 , demonstrated that the CI provided the police with sufficiently reliable information to support the magistrate's probable cause determination. 8

Order allowing motion to suppress reversed .