Opinion for the Court filed by Circuit Judge EDWARDS.
Separate opinion, concurring in part and dissenting in part, filed by Circuit Judge MIKVA.
These three appeals seek the reversal of convictions, based largely on the fruits of electronic surveillance authorized under the District of Columbia Code (“D.C.Code”),1 for violations of the federal Controlled Substances Act.2 Because the. appellants present common questions concerning the Government’s compliance with the D.C. Code’s wiretapping provisions, we resolve all three appeals in this opinion. For the reasons set forth below, we reject each of the grounds on which the appellants urge suppression of the electronically obtained evidence,3 and we affirm the convictions.
*35I. Background
On June 9, 1980, Assistant United States Attorney C. Madison Brewer applied to District Judge Joyce Hens Green for an order permitting the Metropolitan Police Department to intercept communications to and from appellant Wooten’s home phone concerning “the unlawful possession, manufacture and sale of narcotic drugs” in violation of the D.C.Code.4 Because the supporting affidavit was submitted by a nonfederal official, Detective William Larman, and the surveillance was to be conducted by the local police, the application was made under the D.C.Code rather than under Title III of the Omnibus Crime Control and Safe Streets Act of 1968 (“Title III”), 18 U.S.C. §§ 2510-2520 (1976 & Supp. IV 1980).5 Judge Green was informed, however, that, if the wiretap was successful, “evidence ... [would] be presented to a Federal Grand Jury for its consideration of violations of 21 U.S.C. §§ 841(a), 843(b), and 846 (distribution and possession with intent to distribute, use of a telephone facility, and conspiracy).”6
Before filing his application, Brewer submitted the proposed order and supporting documentation to United States Attorney Charles Ruff for his approval. Although Ruff did not approve Brewer’s application in writing, the record reveals,7 and the appellants conceded in the oral argument before this court, that Ruff actually authorized the application. Pursuant to established Justice Department policy,8 Ruff then directed Brewer to seek the approval of the Attorney General or a specially designated Assistant Attorney General.9 Assistant Attorney General Phillip Heymann subsequently authorized the application in a letter to Ruff, which Brewer appended to the document filed with Judge Green.10 Notwithstanding the incorrectness of Brewer’s statement that “[t]he memorandum of authorization signed by Mr. Ruff is attached to this application,”11 Judge Green entered an order permitting wiretapping by the Metropolitan Police, specifically noting probable cause for local narcotics offenses relating to heroin and cocaine trafficking.12
During the period covered by the June Order, the Metropolitan Police intercepted a large number of calls discussing narcotics trafficking and at least one call referring to Preludin (phenmetrazine), a nonnarcotic schedule III controlled substance,13 arrested three persons, and seized 1600 tablets of Preludin. Because the goals of the intercept had not been fully realized, Brewer applied for an extension of the Order on July 9. The Justice Department’s internal authorization procedure for this application paralleled that used for the June Application,14 and Judge Green’s Order recited that the interception had been authorized by “Assistant Attorney General ... M. Carr Ferguson, and his designee, . .. Charles F.C. Ruff, U.S. Attorney for the District of Columbia.”15
Like the initial request for permission to wiretap, the July Application informed *36Judge Green that federal prosecutions were likely.16 The accompanying affidavit, moreover, indicated that the wiretap had provided evidence of trafficking in heroin, cocaine, Preludin, and other drugs, and had enabled officers to seize a large quantity of Preludin.17 Nevertheless, Judge Green’s Order did not explicitly mention Preludin; like the original Order, it referred to “a narcotic operation involving heroin and cocaine.” 18
When the period of interception authorized by the July Order expired on August 8, 1980, the tapes were prepared for sealing and placed in a police safe in a condition that ensured that they would not be tampered with or disclosed.19 They were not judicially sealed, however, until August 13, four-and-one-half days later. The principal reason for the delay was that Judge Green was unavailable. Brewer did attempt to contact District Judge John Penn, the motions judge to whom he believed the matter had been referred, but this effort was frustrated by the emergency appeals that occupied Judge Penn’s schedule. Brewer made no effort to contact other judges at either their offices or their homes.
On March 31, 1981, the appellants were indicted by a federal grand jury as members of a conspiracy to distribute and to possess with intent to distribute Preludin in violation of 21 U.S.C. § 846 (1976). Appellants Gerald Johnson and Wooten were also charged with possessing Preludin with an intent to distribute and using a telephone to commit and facilitate the crimes, in violation of 21 U.S.C. §§ 841(a) and 843(b) (1976). After moving unsuccessfully to suppress the evidence derived from the wire intercepts,20 the appellants were convicted as charged in stipulated nonjury trials. These appeals, which challenge District Judge John Pratt’s denial of the motion to suppress, followed.21
II. Discussion
Appellants urge suppression of the wiretap evidence and reversal of their convic*37tions on the basis of a number of alleged violations of the D.C.Code. They argue that (1) Brewer’s applications for permission to intercept their conversations were not properly authorized, (2) Judge Green lacked jurisdiction to approve electronic surveillance in an investigation of local offenses conducted solely by local officials, (3) the availability of other effective investigative techniques rendered wiretapping unnecessary, (4) the intercepted communications were improperly used to secure convictions for offenses not targeted for investigation, (5) the Government failed adequately to explain its delay in sealing the tapes upon the termination of the surveillance, and (6) the United States Attorney did not comply with the D.C.Code’s annual reporting requirement. We will address these contentions in order. Before doing so, however, we must expound the standards governing the suppression of intercepted communications under the D.C.Code.
A. Standards Governing Suppression
1. Introduction
An “aggrieved person”22 may secure the suppression of wire or oral communications intercepted pursuant to the D.C.Code and evidence derived therefrom if:
(1) the communication was unlawfully intercepted;
(2) the order of authorization or approval under which it was intercepted is insufficient on its face;
(3) the interception was not made in conformity with the order of authorization or approval;
(4) service was not made as provided in section 23-547; or
(5) the seal prescribed by section 23-549(a) is not present and there is no satisfactory explanation for its absence.23
The challenges raised in these appeals implicate only two of these potential grounds for suppression. One concerns subsection (1), which requires suppression only if communications are “unlawfully intercepted.”24 Before turning to the particular grounds for suppression, we will first seek to elucidate the meaning of “unlawfully intercepted.”
The other challenge concerns subsection (5), which requires a determination whether *38the Government offered a “satisfactory explanation” for the delay in securing a judicial seal for the tapes. This second ground will be discussed in Part II.B.4. infra.
2. The Meaning of “Unlawfully Intercepted”
In construing the phrase “unlawfully intercepted,” we look first to the statutory language that Congress used to express its intent.25 Fidelity to Congress’ literal language, always a primary goal of statutory construction, is especially important in interpreting the D.C.Code’s wiretapping provisions, which constitute a comprehensive scheme for regulating the interception of wire and oral communications.26 The statute’s broad scope justifies our assumption that Congress drafted the District’s wiretapping law, like its federal counterpart, “with exacting precision.”27 As a result, “the exact words of the statute provide the surest guide to determining Congress’ intent.” 28
The meaning of the phrase “unlawfully intercepted,” however, is not self-evident, and nowhere in either the wiretapping statute or its legislative history did Congress undertake to define it.29 The Conference Report, for example, specified the grounds for suppression, but did not explain them.30 And while the House Report indicated that “[t]he proposed sections conform virtually word for word with the corresponding sections of the federal wiretap law incorporating the identical procedural safeguards, protections, and restrictions,”31 the legislative history of the federal statute is similarly unhelpful.32
If we were writing on a clean slate, we might feel free to balance Congress’ dual goals—“protecting] effectively the privacy of wire and oral communications” and “aid[ing] ... law enforcement and the administration of justice,”33—by holding that communications are “unlawfully intercepted” whenever the Government fails to comply precisely with any of the procedures established by the wiretapping statute. Under this reading, however, sections 551(b)(2) through 551(b)(5) would be “drained of meaning,” United States v. Chavez, 416 U.S. 562, 575, 94 S.Ct. 1849, 1856, 40 L.Ed.2d 380 (1974), and would become mere surplusage, United States v. Giordano, 416 U.S. 505, 526, 94 S.Ct. 1820, 1831, 40 L.Ed.2d 341 (1974). Although Congress may have intended just such redundancy,34 the Supreme Court has held that it *39did not,35 and we can perceive no special local interest justifying a conclusion that Congress intended the phrase “unlawfully intercepted” to have a different meaning under the District of Columbia’s wiretapping statute than under Title III.36
Our analysis of the legality of the interceptions must begin, therefore, with the Supreme Court’s opinions in Giordano and Chavez, which held that not “every failure to comply fully with any requirement provided in Title III would render the interception of wire or oral communications ‘unlawful.’ ” United States v. Chavez, 416 U.S. at 574-75, 94 S.Ct. at 1855-1856. “To the contrary, suppression is required only for a ‘failure to satisfy any of those statutory requirements that directly and substantially implement the congressional intention to limit the use of intercept procedures to those situations clearly calling for the employment of this extraordinary investigative device.’ ” United States v. Donovan, 429 U.S. 413, 433-34, 97 S.Ct. 658 (1977) (quoting United States v. Giordano, 416 U.S. at 527, 94 S.Ct. at 1832). Implicit in the Court’s opinions, which devote considerable attention to the purposes underlying the statutory requirements at issue, is the principle that violations of even these central requirements do not mandate suppression if the Government demonstrates to the court’s satisfaction that the statutory purpose has been achieved despite the violation.37 We will focus our inquiry on these considerations in determining whether the communications that led to the appellants’ convictions were “unlawfully intercepted” within the meaning of section 551(b)(1).38
B. Possible Grounds for Suppression
1. Defective Authorization
The appellants’ principal objection to the wiretapping procedures followed by the Government in these cases is that the United States Attorney failed to authorize Brewer’s applications in writing as required by D.C.Code Ann. § 23-546(a) (1981).39 *40Section 546(a), its legislative history reveals, was intended to ensure that “[c]ontrol over all ‘wiretapping’ and ‘bugging’ activity in the first instance ... rest[s], directly or indirectly, in the hands of the U.S. attorney.”40 It is clear, therefore, that the United States Attorney for the District of Columbia41 “is the only person who may authorize an application ... for electronic surveillance, consistent with the intent of Congress to centralize policy control ... in the chief prosecuting officer.”42 It is beyond cavil, moreover, that this limitation of the “publicly responsible officials],” 43 who may authorize electronic surveillance under the D.C.Code is a “central or functional safeguard,” United States v. Chun, 503 F.2d 533, 542 (9th Cir.1974), the violation of which requires suppression of intercepted communications.44
Section 546(a)’s requirement that the United States Attorney’s authorization be given in writing is more difficult to characterize. Although one could argue that an oral authorization amounts to no authorization at all, several factors suggest that Congress may have envisioned that the writing requirement would play “[n]o role more significant than a reporting function designed to establish on paper that one of the major procedural protections of ... [the wiretapping legislation has] been accomplished.” United States v. Chavez, 416 U.S. 562, 579, 94 S.Ct. 1849, 1858, 40 L.Ed.2d 380 (1974). We are not unimpressed by the fact that Congress chose to impose a writing requirement in the D.C.Code, but we do not believe that the mere difference in language between the D.C.Code and Title III indicates that a violation of the writing requirement of section 546(a) automatically demands suppression. Significantly, the legislative history is silent on the purpose of the writing requirement,45 and the model act from which the requirement derived provides no clues as to the intended consequences of a violation.46 A more limited role for the writing requirement is also consistent with the D.C.Code’s provisions governing the contents of applications and court orders: An officer seeking permission to wiretap need not inform the court that the United States Attorney’s authorization was given in writing or submit written authorization with his application,47 and the court need not determine that the United States Attorney authorized the application in writing.48
On the present facts, we need not answer the difficult question whether section 546(a)’s writing requirement was intended to occupy a central or functional role in guarding against unwarranted use of electronic surveillance. The record indicates,49 the District Court concluded, at *41least implicitly,50 and the appellants conceded during the oral argument before this court, that United States Attorney Ruff not only actually authorized the applications, but also, pursuant to established Justice Department policy, sought and received the authorization of two Assistant Attorneys General who had been specifically designated to approve federal wiretap applications.51 Under these circumstances, both the overarching purposes of section 546(a)—ensur-ing uniformity and political accountability—and the more limited evidentiary function of the writing requirement were clearly satisfied. Since there is no suggestion that the Government deliberately ignored section 546(a)’s writing requirement, our conclusion that the section’s purposes have been fully satisfied disposes of the appellants’ challenge.
2. Jurisdiction of the District Court
Appellants’ second contention, that the District Court lacks jurisdiction to authorize electronic surveillance in an investigation of local offenses conducted solely by local officials, is meritless. As the appellants have conceded, D.C.Code Ann. § 23-547 (1981), read together with D.C.Code Ann. § 23-541(7) (1981), explicitly authorizes the issuance of wiretap orders by “a judge of the United States District Court for the District of Columbia.”52 Appellants’ secondary thrust—that the inconsistency between the only reasonable construction of the D.C.Code and Title III53 requires us to reject that reading—can be easily parried: Under D.C.Code Ann. § 23-556(b) (1981), the specific authorization provided by the local statute prevails over the more general jurisdictional allocation of Title III.
3. Availability of Normal Investigative Techniques
Appellants also maintain that the Government’s application for judicial authorization to intercept their communications could not support the District Court’s conclusion that “normal investigative procedures have or would have been tried and have or had failed or reasonably appear or appeared to be unlikely to succeed if tried or to be too dangerous.”54 Congress promulgated this necessity requirement to ensure “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, 94 S.Ct. 977, 983 n. 12, 39 L.Ed.2d 225 (1974). This purpose can be achieved, we have previously recognized, only by “giv[ing] close scrutiny to applications challenged for noncompliance and ... rejectpng] generalized and conclusory statements that other investigative procedures would prove unsuccessful.” United States v. Williams, 580 F.2d 578, 588 (D.C.Cir.) (footnotes omitted), cert. denied sub nom. Lincoln v. United States, 439 U.S. 832, 99 S.Ct. 112, 58 L.Ed.2d 127 (1978). The Government need show, however, only that “ ‘other techniques are impractical under the circumstances and that it would be unreasonable to require pursuit of those avenues of investigation.’ ” Id. (quoting United States v. Vento, 533 F.2d 838, 849 (3d Cir.1976)).
Read as a whole, the affidavit accompanying the Government’s wiretapping application 55 was neither superficial nor conclusory. It revealed that the wiretap was sought only after more than six months of extensive investigation, discussed a number of techniques that had been tried or con*42sidered, and amply demonstrated the need for electronic surveillance in this particular investigation,56 We can thus find no reason to reject the District Court’s conclusion that the Government satisfied the D.C.Code’s necessity requirement.
4. Delay in Sealing the Recordings
Appellants next contend that the Government did not offer a “satisfactory explanation” for its four-and-one-half day delay in sealing the tapes. D.C.Code Ann. § 23-549(a) (1981) mandates the acquisition of a judicial seal immediately after the termination of a wiretapping order, and section 551(b)(5) makes the absence of a seal without a satisfactory explanation a ground for suppression. Although the latter provision specifically refers only to the “absence” of a seal, an untimely sealing must also be explained to avoid suppression. United States v. Gigante, 538 F.2d 502, 507 (2d Cir.1976). Because it appears that the District Court may have given too much weight to the fact that “[t]here has been no claim that there has been bad faith or that the tapes were altered or that defendants were in any way prejudiced by the delay,”57 we take this opportunity to clarify the applicable suppression standard.
Relying on a line of cases from the Third, Fifth, and Seventh Circuits,58 the Government appears to argue that an unexplained delay does not require suppression unless the appellants present evidence of actual tampering with the tapes. “To demand such an extraordinary showing, however, would vitiate the Congressional purpose in requiring judicial supervision of the sealing process.” United States v. Gigante, 538 F.2d at 505. As an exhaustive survey of the art concerning the authentication of magnetic tapes for legal purposes concluded, “[tjapes that are made for use in criminal investigations can be falsified, even by relatively unskilled persons, in ways that are superficially convincing. The necessary equipment is readily available, and the necessary techniques are easily learned.”59 Such alterations, moreover, are likely to go undetected because
a highly skilled forensic examiner who is an expert in the fields of tape recording, signal analysis, and speech communication, using the best available analysis equipment, can take weeks and even months to establish with reasonable certainty the fact that a tape has been falsified. The advantage, in terms of effort, time, and cost is clearly with the forger.60
The judicial sealing requirement obviates the need for such costly and inconclusive examinations by providing “an external safeguard against tampering with or manipulation of recorded evidence.” United States v. Gigante, 538 F.2d at 505.61 Although we consider the possibility that the *43tapes have been altered relevant to the assessment of the adequacy of the Government’s explanation for its delay, see United States v. McGrath, 622 F.2d 36, 42 (2d Cir. 1980); United States v. Diana, 605 F.2d 1307, 1314 (4th Cir.1979), cert. denied, 444 U.S. 1102, 100 S.Ct. 1067, 62 L.Ed.2d 787 (1980), we reject any suggestion that it is incumbent upon the potentially aggrieved persons to present evidence constituting a colorable challenge to the integrity of the tapes. Rather, we hold that, in most cases, evidence from which the court can infer that the tapes were held in such a condition as to ensure that they could not be tampered with will be an important component of the Government’s “satisfactory explanation.” If the Government cannot present such evidence, its explanation will be highly suspect.
Here, the record reveals,62 and the appellants have conceded, that the tapes were placed in a police vault in a condition that guaranteed their integrity. This, coupled with the brevity of the delay and the fact that Judge Penn’s unavailability frustrated the Government’s efforts to obtain a judicial seal,63 leads us to accept the District Court’s conclusion that the delay was satisfactorily explained.
5. Use of Intercepted Communications to Secure Convictions for Federal Offenses
Because Judge Green authorized the wiretap to secure evidence concerning heroin and cocaine trafficking in violation of the D.C.Code and its fruits were eventually used to secure federal convictions for trafficking in a nonharcotic drug, the appellants maintain that the Government violated the D.C.Code’s “other crimes” provision, D.C.Code Ann. § 23-548(b) (1981), which requires judicial authorization for the disclosure and use of intercepted communications “relating ... to offenses other than those specified in the order of authorization.” Even if the crimes for which the appellants were convicted were ones for which section 548(b) required separate judicial authorization,64 a conclusion that we need not reach to decide this case, we would not suppress the intercepted communications.
The affidavit accompanying the July Application clearly informed Judge Green of the interception of evidence relating to the offenses for which the appellants were prosecuted.65 This, combined with the Government’s clear statement of its intention to seek federal indictments66 and the fact that the crimes under consideration are very similar, satisfied section 548(b) under the implicit authorization rule adopted by a number of courts interpreting 18 U.S.C. § 2517(5) (1976), Title Ill’s “other offense” provision. Under that rule, “the disclosure in subsequent affidavits to the issuing judge of material facts constituting or clearly relating to other offenses” satisfies the Government’s obligation to seek judicial authorization for the disclosure and use of evidence inadvertently intercepted.67
We note also our uncertainty as to whether suppression would be appropriate if we concluded that the Government had technically violated section 548(b). That section was designed, like its federal counterpart, to deter abuse of wiretapping procedures by guaranteeing that “the original order was lawfully obtained, that it was sought in good faith and not merely as a subterfuge search, and that the communication was in fact incidentally intercepted during the course of a lawfully executed *44order.”68 Because we perceive no reason why the Government would disguise a search for evidence of Preludin distribution as a search for evidence of trafficking in heroin and cocaine, we would conclude that the purposes of section 548(b) were satisfied and that suppression would not be required under the standards we deem appropriate. See Part II.A. supra.
6. Failure to File Annual Reports
The appellants’ final allegation— that the Government’s failure to file the annual reports specified by D.C.Code Ann. § 23-555(b) (1981) requires suppression—is groundless. It does not clearly appear from the record that the United States Attorney failed to file a required report, and, in any event, suppression of the fruits of electronic surveillance would be an inappropriate remedy for a violation of this noncentral provision.69
III. Conclusion
Because the procedures followed by the Government here were deficient in several respects, we take this opportunity to remind it that “strict adherence ... to the provisions of ... [the wiretapping statute] would ... be more in keeping with the responsibilities Congress has imposed upon it when authority to engage in wiretapping or electronic surveillance is sought.” United States v. Chavez, 416 U.S. 562, 580, 94 S.Ct. 1849, 1858, 40 L.Ed.2d 380 (1974). For the reasons set forth above, however, we hold that the District Court did not err in denying the appellants’ motion to suppress. Accordingly, their convictions are
Affirmed.