The defendant was convicted of trafficking in cocaine and heroin in amounts exceeding 200 grams, and of possessing controlled substances with intent to distribute in a school zone. G. L. c. 94C, §§ 32E (b) (4), (c) (4), and 32J. *214Prior to trial, he moved to suppress drugs and drug paraphernalia seized from an apartment pursuant to a search warrant containing a provision permitting the police to enter and search the apartment without first knocking, announcing their presence, and stating their purpose (the “no-knock provision”). The motion was denied and the evidence introduced at his subsequent trial. On appeal, the Appeals Court reversed the motion judge’s denial of the motion to suppress, holding that the affidavit on which the warrant issued was inadequate to support the no-knock provision, and that even if the no-knock provision had been properly included in the warrant, it became ineffective when the search was executed because the exigencies claimed in the affidavit no longer existed. Commonwealth v. Jimenez, 53 Mass. App. Ct. 902 (2001). We granted the Commonwealth’s application for further appellate review. Because we conclude that the circumstances justifying the inclusion of the no-knock provisions were not present at the time of the search, the motion should have been allowed, and the items seized suppressed.
1. Facts. We glean the following facts from the affidavit submitted in support of the warrant application and from the undisputed testimony adduced at the hearing on the motion to suppress.
On November 24, 1997, a search warrant with a no-knock provision was issued on the application of Sergeant Thomas Gaffney of the Worcester police department for an apartment occupying the third floor of a residence at 5 Eastern Avenue in Worcester, and for any persons who might be found on that premises. The property sought included heroin, drug distribution paraphernalia, financial records, money, and documents pertaining to the occupancy of the apartment. The application for the search warrant was the product of several months of police work including the collection of informant information, the execution of a controlled buy, and extensive use of police surveillance. The investigation focused on two individuals nicknamed Papo (later identified as codefendant Jose Carro), and Hector (later identified as the defendant), and a white Chevrolet Lumina automobile that they apparently used to make drug deliveries.
As set forth in the affidavit of Sergeant Gaffney, Papo and *215Hector operated their drug-selling business in a secretive manner. In order to purchase drugs from them, one needed to “beep” a specific telephone number. By a return telephone call, the order would be taken and directions given to a location where the drugs would be delivered. The location at which the drugs were stored and processed for distribution was never made known to the buyers, and was only discovered through police surveillance of the white Lumina after it was used to make deliveries. During the three-month period of police surveillance, Papo and Hector moved their operation from another location to the apartment at 5 Eastern Avenue.
After obtaining the search warrant, the police conducted two days of additional surveillance at 5 Eastern Avenue. At 6:23 p.m. on November 26, 1997, after observing both suspects enter the apartment, the police proceeded to execute the warrant. At the time of execution, it was dark; the suspects were not seen at the windows in the apartment; there were no apparent lookouts; the front door to the building that led to a common hallway and staircase and that normally required a key to open, gave way to “a little push”; and the officers proceeded up the stairs, breaking down the door to the apartment with a battering ram as they announced their presence.1 Papo and the defendant were present in the apartment and were arrested.
The search proved productive. Heroin and cocaine were seized, as was equipment for their processing, packaging, and distribution. Also seized were pagers, $3,099 in cash, a handgun, and thirty-seven rounds of ammunition.
2. Discussion. The requirement that police “knock and announce” their presence and purpose prior to the execution of a search warrant has long been a part of our common law. Commonwealth v. Macias, 429 Mass. 698, 700 (1999). See Commonwealth v. Antwine, 417 Mass. 637, 638 (1994) (holding that, as general rule, police “must knock, announce their identity, and state their purpose”); Commonwealth v. Scalise, 387 Mass. 413, 418 n.5 (1982) (applying rule to search warrant *216as well as arrest warrant); Commonwealth v. Cundriff, 382 Mass. 137, 140-147 (1980), cert. denied, 451 U.S. 973 (1981) (tracing roots of common-law knock and announce rule to Seventeenth Century England). It has also been incorporated into the protections afforded by the Fourth Amendment to the United States Constitution against unreasonable searches. Wilson v. Arkansas, 514 U.S. 927, 934 (1995) (common-law knock and announce principle is “element of the reasonableness inquiry under the Fourth Amendment”). “Among the purposes of this mle are the protection of individual privacy interests and the desire to minimize the potential for violence or property damage.” Commonwealth v. Macias, supra at 701. See Richards v. Wisconsin, 520 U.S. 385, 393 n.5 (1997); Commonwealth v. Cundriff, supra at 140-141.
It is equally well established that the failure of the police to knock and announce their presence may be justified in circumstances where concern for the safety of the officers executing the warrant or fear that a substantial portion of the evidence sought might be destroyed or secreted is present.2 See Commonwealth v. Macias, supra at 701; Commonwealth v. Antwine, supra at 639; Commonwealth v. Scalise, supra at 418; Commonwealth v. Cundriff, supra at 147 n.15. See also Wilson v. Arkansas, supra at 936. In order to justify suspension of the knock and announce requirement, the Commonwealth must establish that there is probable cause to believe that, in the particular circumstances of the search to be undertaken, evidence will be destroyed or officer safety put at risk if the mle is observed. Commonwealth v. Macias, supra at 701, 703.3 This showing must ordinarily be made in advance of the search *217by affidavit submitted to the magistrate at the time of the warrant application. Commonwealth v. Scalise, supra at 420. See Commonwealth v. Benlien, 27 Mass. App. Ct. 834, 835 (1989). Such a showing can also be made after the fact, even if the warrant did not authorize a no-knock entry, if exigent circumstances arise at the threshold of the search justifying both the unannounced entry and the failure to obtain prior judicial authorization. Commonwealth v. Scalise, supra at 422 n.8. Even a no-knock entry properly authorized in advance of a search may turn out to be unlawful if the situation actually encountered by the police at the time of the warrant’s execution is less exigent than what was anticipated. Consequently, the police who execute a search warrant that dispenses with the knock and announce requirement must make a “threshold reappraisal” of the actual circumstances they face before they may disregard the requirement. Id. at 421. Commonwealth v. Macias, supra at 704. Commonwealth v. Benlien, supra at 837. Cf. Richards v. Wisconsin, supra at 395 (“reasonableness of the officers’ decision [to enter without knocking and announcing] must be evaluated as of the time they entered the [premises]”).
In the present case, the Commonwealth attempted to demonstrate that the safety of the executing officers would be jeopardized and evidence might be destroyed if the officers were required to knock and announce their presence and purpose. To this end, the affidavit submitted in support of the warrant application included information that the suspects kept secret the location of the apartment where they stored their drugs, and moved it at least once during the period of police surveillance; that the apartment was located on the third floor of a residential building whose street-level door was kept locked; that it was not possible to approach the building without being seen; that heroin and cocaine could easily be disposed of by flushing them down the toilet; and that it was “common” for *218drag dealers to have firearms and for firearms to be confiscated in the execution of search warrants of this type.
In authorizing the no-knock execution of the warrant, the magistrate did not indicate whether it was justified on the basis of officer safety, likely destruction of evidence, or both. In denying the motion to suppress, the judge identified as “unique facts” supporting the request for the no-knock provision that there would be two suspects in the apartment; that it would be difficult to enter the building; that the officers’ presence would become known before they reached the third-floor apartment; and that the drags were stored in the apartment in secret. On the basis of these findings, he concluded that the affidavit adequately demonstrated both safety concerns and concerns that contraband would be destroyed. The judge made no findings regarding whether the circumstances as they existed at the time of the search continued to justify dispensing with the knock and announce requirement, even though that issue had been specifically raised by the defendant, and much of the hearing on the motion to suppress was devoted to taking testimony on that point.
We accept the judge’s subsidiary findings absent clear error but conduct an independent review of his ultimate findings and conclusions of law. Commonwealth v. Thomas, 429 Mass. 403, 405 (1999). We also acknowledge that affidavits in support of search warrants are to be approached with a view toward common sense, read in their entirety and with considerable latitude allowed for the drawing of inferences. Commonwealth v. Smith, 370 Mass. 335, 342-343, cert. denied, 429 U.S. 944 (1976), quoting Commonwealth v. Perada, 359 Mass. 147, 149 (1971). Here, the judge’s acceptance of the affidavit’s contents as establishing probable cause based on facts uniquely present in the particular circumstances can be sustained as to the likely destruction of evidence, but not as to the presence of safety concerns. More importantly, the uncontested evidence as to the conditions existing at the time of the search require that his ultimate ruling denying the motion be reversed.
First, with respect to concerns for safety, the affidavit described only general concerns present in the execution of any warrant authorizing a search for drags. While it may be true, as *219the affiant asserts, “[tjhat it is common today for drug dealers to be in possession of firearms,” and that firearms are “commonly confiscated” in the execution of searches for drugs, these categorical assertions do not justify dispensing with a review of the specific circumstances present in each case.4 To conclude that such general averments are adequate would amount to the adoption of a per se rule that safety concerns sufficient to warrant suspension of the knock and announce requirement are demonstrated merely by the fact that the search is for drugs. Such a rule was rejected by the Supreme Court in Richards v. Wisconsin, 520 U.S. 385, 390 (1997), as being inadequate to satisfy even the lower standard of reasonable suspicion that the dissent urges us to adopt and that is the minimum required by the Fourth Amendment. Id. at 390.
In Richards v. Wisconsin, supra, the Supreme Court reviewed a ruling of the Supreme Court of Wisconsin that the reasonableness requirement of the Fourth Amendment to the United States Constitution was satisfied by a per se exception to the knock and announce rule in the execution of search warrants in felony drug investigations. In reaching its ruling, the Wisconsin court found it reasonable to assume, based on studies, articles, and judicial opinions, that felony drug searches involve “an extremely high risk of serious if not deadly injury to the police.” Id. at 390. Accordingly, it concluded that the police do not need to demonstrate specific information about dangerousness in order to dispense with the knock and announce requirement in such searches. Id. In rejecting this holding, the Supreme Court held that even though “felony drug investigations may frequently present circumstances warranting a no-knock entry,” *220it is “the facts and circumstances of the particular entry [which must justify] dispensing with the knock-and-announce requirement.” Id. at 394.
While the affidavit here contained a great deal of detail about the defendant’s drug operation, it contained no particular facts and circumstances suggesting that there might be weapons on the premises, that the defendant or the codefendant might carry or possess weapons, or that either had a history of weapons possession or violence. Without more, the affidavit was inadequate to establish probable cause (or even reasonable suspicion) that the officers’ safety would be jeopardized by requiring them to knock and announce their presence before executing the warrant. Commonwealth v. Hernandez, 49 Mass. App. Ct. 911, 913 (2000).5
The circumstances presented in the affidavit with regard to the likelihood of destruction of evidence lead us to a different conclusion. While the fact that drugs can often readily be disposed of in a sink or toilet is not an adequate basis on which probable cause can be found, Commonwealth v. Scalise, 387 Mass. 413, 421 (1982), it is, of course, an obvious and important factor that the magistrate may consider along with other reasons for tipping the balance and justifying an exception to the knock and announce rule. Foremost among such other reasons is the likelihood that the occupants of the dwelling will have advance knowledge of the officers’ presence and purpose. Here, the information set forth in the affidavit specifically raises this likelihood in its description of the premises as having *221(1) windows overlooking the approach that the police would need to traverse in order to gain entry to the building, and (2) a locked door located several floors below the apartment to be searched. These facts, when combined with the secretive manner of the drug operation and the movement of its locus during the period of police surveillance, would adequately support inferences drawn by the magistrate that the suspects would likely notice a police presence before the police ever got to the point where the knock and announce requirement would apply,6 and that they would be prepared to dispose of the drug evidence within the premises as soon as they learned of that presence. Considering these inferences together, we conclude that the magistrate’s approval of the no-knock provision was supported by probable cause to believe that the extra time afforded the occupants of the apartment by requiring the police to knock and announce their presence “would allow a significant additional portion of the evidence sought to be destroyed.” Commonwealth v. Macias, 429 Mass. 698, 703 (1999). See Commonwealth v. Scalise, supra at 419, 421 & n.7 (furtive conduct and suspect’s likely awareness of police surveillance adequate basis for no knock); Commonwealth v. Benlien, 27 Mass. App. Ct. 834, 836 (1989) (set up of apartment permitting lookout for police combined with physical obstacle to entry adequate basis for no knock). But see Commonwealth v. Macias, supra (apartment windows overlooking buzzer-operated front door insufficient to establish probable cause that extra time would result in substantial additional evidence being destroyed where large quantity of drugs stored in different parts of apartment and packaged in many smaller plastic packages would be difficult to dispose of quickly).
Having concluded that the warrant was properly issued, we turn to its execution. As noted, the police timed the execution of *222the warrant to coincide with the presence of both suspects in the premises, presumably to ensure the search of their persons and their arrest if contraband was found during the search. The warrant was executed after dark, there was no lookout, and the suspects were not at the windows of the apartment. Every indication was that the officers would not be and were not observed approaching the building. In addition, the locked door on the first floor merely opened when pushed and did not present any obstacle or delay to entering the building, or provide any apparent notice to the suspects three floors above. In sum, when the police arrived at the threshold of the apartment to be searched, there was no basis to believe that the occupants might have notice of their presence and might therefore be destroying evidence. The most relevant concerns set forth in the affidavit, the likelihood of being observed approaching the building and the delay likely to be encountered in breaking through the locked door on the first floor, proved not to be present at the time of execution. These are precisely the type of circumstances that require a reappraisal of the legitimacy of a no-knock entry. On these facts, such entry was no longer warranted and was therefore unlawful.
The fact that an unlawful search has occurred does not automatically result in the exclusion of any illegally seized evidence. Commonwealth v. Grimshaw, 413 Mass. 73, 78 (1992), quoting Commonwealth v. Gomes, 408 Mass. 43, 46 (1990). The Commonwealth, however, has not pointed to any reason in its brief or argument why exclusion should not be the remedy in this case. The evidence seized in the apartment should have been suppressed. Because there could not have been a valid conviction without the impermissible evidence, the judgments are vacated, the verdicts set aside, and judgments shall enter for the defendant.
So ordered.
The Commonwealth does not contend that the police complied with the knock and announce requirement by calling out “police” as they proceeded to batter down the door. See, e.g., Commonwealth v. Gomes, 408 Mass. 43, 44, 46 (1990).
Circumstances suggesting that a suspect might escape if given notice of police presence can also be grounds for dispensing with the knock and announce requirement. Commonwealth v. Rodriguez, 415 Mass. 447, 450 (1993). The Commonwealth does not contend on appeal that a risk of escape justified the no-knock provision in this warrant.
In Commonwealth v. Macias, 429 Mass. 698, 701 (1999), we declined to depart from the probable cause standard established in our common law and adopt the reasonable suspicion standard that the United States Supreme Court concluded was required in order to justify a no-knock entry in the execution of search warrants under the Fourth Amendment to the United States Constitution. See Richards v. Wisconsin, 520 U.S. 385, 394-395 (1997). This elevated standard for the unannounced entry into a dwelling is consistent with *217the high degree of privacy that this court has historically held, in other contexts, can be expected in one’s home. See, e.g., Commonwealth v. Blood, 400 Mass. 61, 68-75 (1987) (privacy interests in conversation occurring in home protected by art. 14 of the Massachusetts Declaration of Rights, beyond protection of Fourth Amendment to United States Constitution); Commonwealth v. Panetti, 406 Mass. 230, 234-235 (1989) (conversations in one’s home provided greater privacy protection under art. 14).
While our assessment of the validity of the warrant is confined to the facts set forth in an affidavit that contained no specific factual basis for its assertion that certain events were “common,” we note that during the hearing on the motion to suppress, Sergeant Gaffiiey (the affiant) testified that he participates in one hundred to 120 drug searches each year, and that about thirty to forty firearms are typically found in these searches. Assuming that this is the basis of Sergeant Gaffney’s averment that firearms are “commonly” found in drug searches, it translates into firearms being found between twenty-five and forty per cent of the time. With regard to searches where firearms were found, there was no testimony as to whether in some or all of these instances the police had specific reasons to believe that a suspect might possess weapons before the searches were conducted.
In Commonwealth v. Rodriguez, 415 Mass. 447, 448-451 (1993), we upheld a no-knock entry on grounds of likely destruction of evidence and danger to the officers conducting the search even though there was no specific information that weapons might be present. This decision was issued before Richards v. Wisconsin, 520 U.S. 385 (1997). To the extent that the Rodriguez decision might be read to hold that an affidavit merely stating that in the affiant’s experience handguns are “a danger to law enforcement agents during drug-related searches,” without specific information regarding the search to be undertaken, is an adequate basis for waiver of the knock and announce rule, id. at 451, it is a reading that is no longer apt in light of Richards v. Wisconsin, supra. This is not to say that an affidavit specifically detailing police experience in dealing with drug dealers associated with a particular criminal enterprise or in a particular community (of which the suspects might be a part) would not suffice, but such an affidavit would need more than the general averments contained here.
Such notice would not only give the occupants added time to dispose of the evidence, it would also negate one of the principle purposes of the knock and announce requirement, i.e., to give adequate warning to the occupants that it is the police at the door, so as to avoid surprise which might lead to unnecessary violence. See Commonwealth v. Antwine, 417 Mass. 637, 638-639 (1994) (if person already knows of police presence, knock and announce requirement is “useless gesture” excusing police from full compliance with rule).