During a criminal investigation, the Government secured a series of court orders authorizing electronic surveillance of respondents, as mandated by Title III of the Omnibus Crime Control and Safe Streets Act of 1968, 18 U.S.C. 2510 et seq. Section 2518(8)(a) requires, in pertinent part, that: (1) recording "shall be done in such way as will protect the recording from editing or other alterations"; (2) "[i]mmediately upon the expiration of the period of the order, or extensions thereof," the recordings are to be made available to the judge who issued the order and sealed under his directions; and (3) "[t]he presence of the seal . . . or a satisfactory explanation" for its absence is a prerequisite for the use or disclosure of the evidence obtained from the recordings. Among the orders obtained, was an April 27, 1984, order for the surveillance of respondent Ojeda Rios Levittown, Puerto Rico, residence and some nearby public telephones, which was extended until July 23, when he moved to another community. On July 27, the Government obtained a new order covering his new home, which, with extensions, expired on September 24. On October 13, three days after the expiration of an order authorizing surveillance of Ojeda Rios car, all of the Ojeda Rios tapes were sealed. The Government also obtained an order authorizing it to wiretap two public telephones in Vega Baja, effective January 18, 1985, but that order expired on February 17. A new order, issued on March 1, expired on May 30, and the Vega Baja tapes were sealed on June 15. After they were indicted for various offenses, respondents moved to suppress the evidence obtained as a result of, inter alia, these wiretaps. The District Court suppressed the Levittown and Vega Baja tapes based solely on a delay in their sealing. The court found that the July 27 order authorizing the wiretap of Ojeda Rios new residence was not an extension of the Levittown order, and therefore there was at least an 82-day delay - starting July 23 - in sealing the Levittown tapes. Similarly, the March 1 Vega Baja order could not be considered an extension of the January 18 order, because of the delay in seeking the extension and the Governments failure to satisfactorily explain the delay. Thus, there was a 118-day delay in the sealing of those tapes. The Court of Appeals affirmed. [495 U.S. 257, 258]

Held:

1. Section 2518(8)(a) applies to a delay in sealing as well as to a complete failure to seal tapes. Its primary thrust is to ensure the reliability and integrity of evidence obtained by means of electronic surveillance, and the sealing requirement is important precisely because it limits the Governments opportunity to alter the recordings. The narrow reading suggested by the Government - that since tapes must either bear a seal or the Government must provide a "satisfactory explanation" for the seals "absence," the "satisfactory explanation" requirement does not apply where the tapes actually bear a seal, regardless of when or why the seal was applied - is not a plausible interpretation of congressional intent, since 2518(8)(a) requires not just any seal but one that has been obtained immediately upon expiration of the underlying surveillance order. The Governments view would create the anomalous result that the prosecution could delay requesting a seal for months without risking a substantial penalty. Pp. 262-264.

2. The "satisfactory explanation" language requires that the Government explain not only why a delay occurred but also why it is excusable. The Governments submission - that the requirement is satisfied if it first explains why the delay occurred and then demonstrates that the tapes are authentic - would nullify the requirements function as a safeguard against tampering and is foreclosed by the provisions plain words. The fact that the Government has an i