The defendant, Stephen H. Fenderson, was convicted by a judge of the Superior Court, sitting without a jury, of trafficking in cocaine. General Laws c. 94C, § 32E {b) (2) (1988 ed.). The defendant appeals his conviction, ar*83guing that the motion judge erred in denying his motion to suppress evidence. We affirm.1
The defendant argues that affidavits submitted by the police in support of a warrant authorizing a wiretap of his telephone were defective since they did not show adequately that traditional investigative procedures failed or appeared unlikely to succeed. See G. L. c. 272, § 99 E 3 (1988 ed.). The defendant also claims that a warrant authorizing the search of two safety deposit boxes lacked probable cause. We discuss the facts as they pertain to the two issues raised by the defendant.
1. Failure of normal investigative procedures. General Laws c. 272, § 99 E 3, provides that a warrant authorizing a wiretap may issue only on “a showing by the applicant that normal investigative procedures have been tried and have failed or reasonably appear unlikely to succeed if tried.” This statutory provision is practically identical to the Federal wiretap statute. 18 U.S.C. § 2518 (l)(c) (1990). See Commonwealth v. Vitello, 367 Mass. 224, 259 (1975); Commonwealth v. Wallace, 22 Mass. App. Ct. 247, 248 n.2 (1986). In meeting its statutory burden of establishing necessity, “[t]he Commonwealth need not show that traditional investigative techniques were wholly unsuccessful or that the police had exhausted all other investigative procedures before filing its application for a warrant authorizing a wiretap.” Commonwealth v. Wilson, 405 Mass. 248, 250 (1989). The necessity requirement is meant to “assure that wiretapping is not resorted to in situations where traditional investigative techniques would suffice to expose the crime.” United States v. Kahn, 415 U.S. 143, 153 n.12 (1974). The affidavit will be adequate if it indicates a reasonable likelihood that normal *84investigative techniques have failed in gathering' evidence, or would fail if attempted. United States v. Ashley, 876 F.2d 1069, 1073 (1st Cir. 1989). United States v. Abou-Saada, 785 F.2d 1, 11 (1st Cir.), cert, denied sub nom. Tannous v. United States, 477 U.S. 908 (1986). In determining whether the Commonwealth has met its burden, the affidavit should be read in a “practical and commonsense manner.” United States v. Abou-Saada, supra, quoting United States v. Scibelli, 549 F.2d 222, 226 (1st Cir.), cert, denied, 431 U.S. 960 (1977).
In this case, an affidavit signed by Sgt. Paul Stone, a member of the Norfolk County district attorney’s Drug Task Force (DTF) was presented in support of the wiretap warrant.2 The affidavit stated that three informants provided Stone with information regarding the defendant’s trafficking in narcotics, and a fourth informant made two supervised purchases of cocaine from the defendant. The four informants, however, were unwilling to testify against the defendant or to introduce undercover agents to the defendant because they were afraid of reprisals. See United States v. Gambale, 610 F. Supp. 1515, 1539-1540 (D. Mass. 1985), aff'd, United States v. Angiulo, 847 F.2d 956 (1st Cir.), cert, denied sub nom. Cincotti v. United States, 488 U.S. 852 (1988), and cert, denied sub nom. Angiulo v. United States, 488 U.S. 928 (1988); Commonwealth v. Wilson, supra. Cf. United States v. Ippolito, 774 F.2d 1482, 1486-1487 (9th Cir. 1985) (suppression of wiretap evidence proper where informer willing to testify and had potential for uncovering entirety of conspiracy). The affidavit also explained that visual surveillance of the defendant’s home was attempted, but that, because of the isolated location of the house, extended surveillance was impossible without being detected. The police also unsuccessfully sought information by inspecting the *85defendant’s toll telephone records, and even by going through his garbage. In this context, the use of electronic means of surveillance techniques was not unreasonable. See United States v. Hoffman, 832 F.2d 1299, 1306-1307 (1st Cir. 1987); United States v. Gambale, supra at 1541.
The police had information that the defendant was part of a conspiracy to distribute drugs. Sgt. Stone’s affidavit stated that an informant told the police that the defendant and two other individuals “conducted their drug distribution business out of several area bars.” Another informant stated that the defendant had “supplied several lower-level dealers.” A third informant told the police that the defendant was the “supplier of the suppliers” in the area. The affidavit concluded that a search of the defendant’s home “would likely fail in reaching our broader objectives of discovering the identity of Fenderson’s cocaine suppliers, those who may distribute cocaine for Fenderson, and the locations where cocaine, records, and monies derived from the sale of cocaine may be hidden. ... At this point in the investigation we are not entirely sure where Fenderson keeps his supply of cocaine. It is possible that he uses another location instead of his residence to store the drugs. If that were the case, a search of his residence would be fruitless.” The affidavit stated with sufficient specificity why a search of the defendant’s home probably would not have yielded the information sought by the investigators. See United States v. Rodriguez, 606 F. Supp. 1363, 1368 (D. Mass. 1985).3
*86The affidavit furnished sufficient information to show a reasonable likelihood that traditional investigative techniques either failed or would have failed, if attempted, in providing the police with information regarding the defendant’s drug-trafficking activities.* **4
2. Probable cause. Based on the information gathered through the wiretap of the defendant’s telephone, the police obtained and executed a search warrant of the defendant’s home. During the search, the police found cocaine, marihuana, a shotgun, assorted drug paraphernalia, $1,750 of *87United States currency, and several keys to safety deposit boxes. On that same day, a magistrate signed a warrant authorizing the police to search the safety deposit boxes. The search of one of the boxes yielded $460,000 in United States currency, while the search of a second box yielded $18,000 and personal documents belonging to the defendant. The defendant argues that the magistrate lacked probable cause to issue the warrant authorizing the search of the safety deposit boxes.6
The warrant was issued on the basis of an affidavit signed by Sgt. Stone. The affidavit incorporated by reference the previous affidavits used in support of the wiretap and search warrants. The affidavit stated that large amounts of cocaine and several safety deposit box keys were found in the defendant’s home. The affidavit added that “[o]ur investigation of Fenderson was done largely through the use of electronic surveillance. Through this means we learned that Fenderson was actively engaged in the distribution of cocaine. We also confirmed that Fenderson was not employed throughout this investigation. It is safe to say at this point that he was supporting himself by selling illegal narcotics. We have learned through prior investigations that drug dealers often use safe deposit boxes to hide the proceeds generated by narcotics transactions. This allows them to avoid [detection] by law enforcement authorities.’’ The affidavit concluded that “there is probable cause to believe that these safe deposit boxes contain cocaine, monies derived from the sale of cocaine, or other evidence of cocaine transactions.”
In order to establish probable cause, an affidavit must “contain enough information for the issuing magistrate to de*88termine that the items sought are related to the criminal activity under investigation, and that they may reasonably be expected to be located in the place to be searched.” Commonwealth v. Cefalo, 381 Mass. 319, 328 (1980). “In each case, the basic question for the magistrate is whether he has a substantial basis for concluding that any of the articles described in the warrant are probably in the place to be searched.” Commonwealth v. Upton, 394 Mass. 363, 370 (1985). In evaluating an affidavit, a magistrate may apply his or her common knowledge, while drawing reasonable inferences from the factual information contained in the document. Commonwealth v. Taglieri, 378 Mass. 196, 198, cert, denied, 444 U.S. 937 (1979).
The magistrate, on learning of the information gathered by the police regarding the defendant’s activities in the distribution of drugs, and of the fact that large amounts of cocaine were found in his house, could have applied his common sense and reasonably concluded that the defendant was hiding the profits of his drug trade. This reasonable conclusion, coupled with the fact that keys to safety deposit boxes of a nearby bank were found in the defendant’s home and the fact that in Sgt. Stone’s experience drug traffickers often use safety deposit boxes to hide money, was sufficient to establish probable cause. United States v. Gonzalez, 488 F.2d 833, 838 (2d Cir. 1973) (connection between deposit box and narcotics transaction inferred from officer’s experience and from fact that on day of transaction defendant possessed deposit keys at nearby bank). See Commonwealth v. Taglieri, supra at 198-199. The affidavit contained sufficient information for the magistrate to have concluded reasonably that the articles described in the warrant were inside the safety deposit boxes.
Judgment affirmed.