McGOWAN, Circuit Judge:

Appellant Ramsey was convicted in the District Court on one count of unlawful importation of heroin ( 21 U.S.C. § 952(a) (1970)); three counts of unlawful use of a communication facility ( 21 U.S.C. § 843(b) (1970)); one count of possession of heroin with intent to distribute ( 21 U.S.C. § 841(a) (1970)); one count of unlawful receipt and possession of a firearm (18 U.S.C.App. § 1202(a)(1) (1970)) and one count of unlawful possession of a pistol (22 D.C. Code § 3203 (1973)). Appellant Kelly was convicted on one count of unlawful importation, one count of unlawful use of a communication facility, and one count of possession with intent to distribute. On appeal, a number of allegations of error are made, one of which we find to be of merit, and we therefore reverse the convictions.

I

The case was tried to the District Judge on the basis of a lengthy stipulated record which we need summarize only in broad outline. In November of 1973, Sylvia Bailey and William Ward, who resided in West Germany, were engaged in international narcotics trafficking. They were subjected to electronic surveillance pursuant to a West German court order, and the wiretap led to a search of Ward at the Munich Airport in December of 1973, which turned up no drugs but $10,000 in cash. The wiretap was reactivated in January of 1974, and among the calls intercepted were incriminating trans-Atlantic conversations concerning narcotics between Bailey and appellant Ramsey.

Ward and Bailey travelled to Thailand in late January of 1974, and Thai officials were alerted to their presence by West German agents. The Thai officials placed them under surveillance, and observed Ward mailing letter-sized envelopes in six different mail boxes. Five of these envelopes were recovered, and among the addresses they bore was a mail drop in Washington, D.C. later linked to appellants. On February 2, 1974, Bailey and Ward were arrested in their hotel room in Thailand, and seized in the raid were all the ingredients for the narcotics importation scheme. Among the items so obtained were numerous sealed, heroin-filled envelopes, eleven of which bore Washington, D.C. addresses with which appellants were later found to have a connection.

Two days later in New York — independently and without any knowledge of the foregoing — Customs Inspector George Kallnischkies seized and, proceeding without a warrant, opened eight envelopes found to contain heroin. The envelopes had been mailed from Thailand and were destined for four addresses in the Washington area. These envelopes were resealed and forwarded to Washington, and six were delivered to three addresses. Federal agents witnessed Kelly retrieve all six envelopes, rendezvous with Ramsey at the latter's residence, and transfer to Ramsey a brown paper bag. The agents moved in and arrested both men. The paper bag was found to contain the six letters, $1,100 in cash, and cutting material. Also seized from Ramsey was a notepad with Bailey's phone numbers and addresses. The next day, in executing a search warrant on Ramsey's residence, the agents recovered, inter alia, the two pistols for whose unlawful possession Ramsey stands convicted and a cardboard sheet with Sylvia Bailey's phone numbers.

II

The critical issue in this case, in our view, is the warrantless search of the eight envelopes at the New York Post Office. Those envelopes, and a great deal of evidence deriving from their seizure, were presented before the trier, and no attempt is or could fairly be made by the Government to argue that, if the seizure was illegal under the Fourth Amendment, the error was harmless as to any of the counts. As we proceed to develop, we believe that the opening of these letters without resort to a warrant procedure was a constitutional violation, and the use at trial, over the objection of appellants, of evidence obtained thereby requires overturning the convictions.

Inspector Kallnischkies was a supervisor of Customs Service Inspectors dealing with international letter class mail (the category closest to domestic first class mail). He testified that foreign airmail mail coming to the New York General Post Office is placed on a conveyor belt for sorting, and during that process he would remove any items that looked "suspicious." Tr. of October 25, 1974 Hearing, at 6. In this instance, he removed eight envelopes from the belt because they were from Thailand — a known source of heroin — and were bulky. Id. at 7. He weighed one of the envelopes and found it to weigh 42 grams, roughly three times the weight of a normal letter. Id. at 8-9. The envelope also "felt like there was something in there. . . ." Id. at 9. He then opened one envelope and found a plastic bag containing white powder between some pieces of cardboard. Upon testing, the powder was found to be heroin. The other envelopes also were found to contain heroin.

The Government would place this search within the border search exception to the warrant requirement. The view that packages moving through international mail fall within the border search exception has been uniformly adopted by courts confronting that question. E. g., United States v. Doe, 472 F.2d 982, 984 (2d Cir.), cert. denied, 411 U.S. 969, 93 S.Ct. 2160, 36 L.Ed.2d 691 (1973); United States v. Galvez, 465 F.2d 681, 687 (10th Cir. 1972); United States v. Beckley, 335 F.2d 86, 88-89 (6th Cir. 1964), cert. denied, 380 U.S. 922, 85 S.Ct. 921, 13 L.Ed.2d 807 (1965); United States v. Swede, 326 F.Supp. 533, 535-36 (S.D.N.Y. 1971); United States v. Sohnen, 298 F.Supp. 51, 54-55 (E.D.N.Y. 1969). The last-mentioned court, (Weinstein, J.), indicated that it might reach a different result where letters, rather than packages were involved. United States v. Sohnen, supra, at 55.

However, two circuits have squarely ruled that international letter mail, like international package mail, does fall within the border search exception. United States v. Bolin, 514 F.2d 554, 557 (7th Cir. 1975), citing United States v. Odland, 502 F.2d 148, 151 (7th Cir.), cert. denied, 419 U.S. 1088, 95 S.Ct. 679, 42 L.Ed.2d 680 (1974); United States v. Barclift, 514 F.2d 1073, 1074-75 (9th Cir.) (per curiam), cert. denied, 423 U.S. 842, 96 S.Ct. 76, 46 L.Ed.2d 63 (1975). See also United States v. Francis, 487 F.2d 968 (5th Cir. 1973), cert. denied, 416 U.S. 908, 94 S.Ct. 1615, 40 L.Ed.2d 113 (1974). Both of these circuits rested their analysis on nothing more than the assertion that no meaningful difference could be drawn between the entry of mail into the United States and the entry of automobiles, baggage, individuals, or packages.

In our view, that assertion is sustainable only by embracing the most sweeping concept that the "integrity of our borders" requires that all objects crossing them may be searched at the whim of the Government. If, in fact, we look to the rationale of the border search exception, we find that it is based upon (1) the impracticability of requiring a warrant given the huge volume of items moving across the border likely to contain contraband, e. g., United States v. Doe, supra, at 982-83; Morales v. United States, 378 F.2d 187, 190 (5th Cir. 1967), and (2) the difficulty of obtaining a warrant when the subject of the search is mobile, as a car or person, Carroll v. United States, 267 U.S. 132, 153, 45 S.Ct. 280, 69 L.Ed. 543 (1925).

When we compare letters to persons or automobiles it becomes apparent how little force this rationale carries when applied to letters. There are limited kinds of contraband that can be concealed within a letter-sized envelope; the decided cases appear to involve almost exclusively narcotics, although it is perhaps conceivable that small pieces of jewelry, small quantities of precious metals, or currency might also be concealed. There is, therefore, a smaller likelihood in the first instance that a letter, rather than an automobile or a suitcase, contains contraband. Moreover, as far as the central problem of narcotics is concerned, the Customs Service can effectively use trained dogs who can detect the smell of contraband drugs. See, e.g., United States v. Mitchell, 525 F.2d 1275, 1277 (5th Cir. 1976); United States v. Fulero, 162 U.S.App.D.C. 206, 498 F.2d 748 (1974) (per curiam); United States v. Feldman, 366 F.Supp. 356, 358 (D.Hawaii 1973). Similarly, X-ray examination, or metal detectors like those currently in use at airports, could detect precious metals or jewelry. See, e.g., United States v. Chiarito, 507 F.2d 1098, 1099 (5th Cir.) (per curiam), cert. denied, 423 U.S. 824, 96 S.Ct. 38, 46 L.Ed.2d 40 (1975); United States v. Sohnen, supra, at 53. These techniques could screen out a large percentage of otherwise suspicious mail that, under current practice, is routinely opened. The dimensions of the remaining problem of smuggling in letter-sized envelopes are of a different order than those of other kinds of traffic across the border.

Furthermore, suspicious-looking letters (and, to be sure, packages as well), unlike more mobile automobiles or travellers, can easily be detained to permit further examination (as with dogs, magnetometers, or X-rays) or to obtain a warrant. In United States v. Van Leeuwen, 397 U.S. 249, 90 S.Ct. 1029, 25 L.Ed.2d 282 (1970), the Supreme Court unanimously upheld the authority of officials to detain first class mail for a period of 29 hours while they investigated suspicious circumstances and obtained a search warrant. Given this holding, it would appear to be an a fortiori case for Customs Inspectors to detain international letter mail for a reasonable period in which to investigate and, if appropriate, to obtain a warrant.

It thus seems that searches of international letter mail at best strain the rationale of the border search exception. Like all exceptions to the warrant requirement, see generally, e.g., United States v. United States District Court, 407 U.S. 297, 318, 92 S.Ct. 2125, 32 L.Ed.2d 752 (1972); Coolidge v. New Hampshire, 403 U.S. 443, 454-55, 91 S.Ct. 2022, 29 L.Ed.2d 564 (1971); Jones v. United States, 357 U.S. 493, 499, 78 S.Ct. 1253, 2 L.Ed.2d 1514 (1958), the border search exception must be carefully and narrowly drawn. The Supreme Court has in recent years twice declined to take an expansive view of the border search exception or the authority of the Border Patrol. See United States v. Brignoni-Ponce, 422 U.S. 873, 95 S.Ct. 2574, 45 L.Ed.2d 607 (1975); Almeida-Sanchez v. United States, 413 U.S. 266, 93 S.Ct. 2535, 37 L.Ed.2d 596 (1973). And as in the Court's most recent decision, in the instant case we are "not convinced that the legitimate needs of law enforcement require this degree of interference with lawful traffic." United States v. Brignoni-Ponce, supra, at 883, 95 S.Ct. at 2581.

Finally, and probably most important, letter mail is a vital means of communication in our society. Letters express the most important and sensitive of our personal, familial, political, professional, and financial affairs. They implicate both our deepest privacy and our interest in free expression, far more than packages or suitcases or automobiles. In the words of Justice Holmes, "the use of the mails is almost as much a part of free speech as the right to use our tongues." United States ex rel. Milwaukee Social Democratic Pub. Co. v. Burleson, 255 U.S. 407, 437, 41 S.Ct. 352, 363, 65 L.Ed. 704 (1921) (Holmes, J., dissenting), quoted with approval in Blount v. Rizzi, 400 U.S. 410, 416, 91 S.Ct. 423, 27 L.Ed.2d 498 (1971), and United States v. Van Leeuwen, supra, at 251.

Even if the ordinary practice of the Customs Service is not to read the mail that is opened, see note 9 infra, mere knowledge on the part of individuals of the practice of routinely opening mail inhibits the exercise of free speech. See Procunier v. Martinez, 416 U.S. 396, 423, 94 S.Ct. 1800, 40 L.Ed.2d 224 (1972) (Marshall, J., concurring); cf. Talley v. California, 362 U.S. 60, 65, 80 S.Ct. 536, 4 L.Ed.2d 559 (1960); NAACP v. Alabama, 357 U.S. 449, 462, 78 S.Ct. 1163, 2 L.Ed.2d 1488 (1958). And the Supreme Court has indicated that limits on search and seizure must be especially strong where First and Fourth Amendment values converge. See, e. g., United States v. United States District Court, supra, at 313-14, 92 S.Ct. 2125; Stanford v. Texas, 379 U.S. 476, 485, 85 S.Ct. 506, 13 L.Ed.2d 431 (1965).

The Court has also noted, with reference to the need to enforce Fourth Amendment protections, that "[h]istory abundantly documents the tendency of Government — however benevolent and benign its motives — to view with suspicion those who most fervently dispute its policies." United States v. United States District Court, supra, at 314, 92 S.Ct. at 2135. The recent disclosures about the widespread illegal searches of mail by United States intelligence agencies, see, e. g., Report to the President by the Commission on CIA Activities Within the United States [the Rockefeller Commission], June 1975, at 101-15, 168; S.Rep. No. 755, 94th Cong., 2d Sess., Book II, at 12, 17, 38, 62, 107-08 (1976); id., Book III, at 559-677; Hearings before the Senate Select Comm. to Study Governmental Operations with Respect to Intelligence Activities, 94th Cong., 1st Sess., Vol. 2, at 1-2, 15-16, 51-63, 66, 76 (1975); id., Vol. 4, at 2, 4, 6-7, 10-11, 21-22, 31-35, 38, 43, 148, 150, 163; id., Vol. 6, at 202-06, 367, highlight the importance of the Supreme Court's observation. The Supreme Court has also stated, as one reason supporting its requirement that warrants be obtained for electronic surveillance related to the domestic aspects of national security, that "[b]y no means of least importance will be the reassurance of the public generally that indiscriminate wiretapping and bugging of law-abiding citizens cannot occur." United States v. United States District Court, supra, at 321, 92 S.Ct. at 2139. Routine opening of international mail presents the same threat to First Amendment interests, and enforcing the protections of the Fourth Amendment can provide law-abiding citizens with the same important assurance.

It thus appears that there is not a sufficient need, and there is too great a risk to personal privacy, to extend the border search exception to permit unrestrained opening of international mail. We believe that the values protected by the First and Fourth Amendments demand that, before international letter mail is opened, a showing of probable cause be made to and a warrant secured from a neutral magistrate.

Any suggestion that adherence to the warrant requirement would serve no purpose in a case like the one at bar cannot be sustained. If the suggestion is directed merely against the clear recognition of the independent force of the Fourth Amendment's warrant clause, it cannot be persuasive. And there are at least three distinct functions that a warrant procedure would serve. First, by requiring that the inferences to which law enforcement officials are entitled be drawn by neutral magistrates rather than by officers in the heat of duty, see Johnson v. United States, supra, at 13-14, 68 S.Ct. 367, 368-369, 92 L.Ed. 436, it helps to limit unjustified intrusions upon the private and communicative material contained in letter mail. Second, it creates a record of the circumstances justifying an opening before the search occurs; this record minimizes the burden of post facto judicial review, United States v. United States District Court, supra, at 321, 92 S.Ct. 2125, and sharply limits the possibility that officials will attempt to justify a search by what it turns up rather than what was known beforehand, see, e. g., United States v. Di Re, 332 U.S. 581, 595, 68 S.Ct. 222, 92 L.Ed. 210 (1948). Inspector Kallnischkies' inability to remember precisely the basis upon which he determined to open the letters in question, see note 3 supra, illustrates the importance of this purpose.

Finally, establishment of a warrant machinery is a bulwark against the enlistment of mail openings not on behalf of responsible law enforcement, but rather to serve other, less commendable purposes. In Almeida-Sanchez, the Supreme Court reminded us of Justice Jackson's words shortly after returning from the Nuremberg trials:

These [Fourth Amendment rights], I protest, are not mere second-class rights but belong in the catelog of indispensable freedoms. Among deprivations of rights, none is so effective in cowing a population, crushing the spirit of the individual and putting terror in every heart. Uncontrolled search and seizure is one of the first and most effective weapons in the arsenal of every arbitrary government.

413 U.S. at 274, 93 S.Ct. at 2540, quoting Brinegar v. United States, 338 U.S. 160, 69 S.Ct. 1302, 93 L.Ed. 1879 (1949) (Jackson, J., dissenting). To advert again to the documented abuses by American intelligence agencies in conducting mail searches does not reflect an obsession with current headlines, but rather highlights the importance of our duty to enforce the Fourth Amendment's protection of individual privacy and security.

The Government has suggested that a warrant requirement would be impracticable, but there is absolutely nothing in the record to support this assertion. No proof has been adduced to show, and we have no reason to believe, that using X-ray inspection, metal detectors, specially trained dogs, and the like to dispel suspicion, raised by external appearance, that a letter contains narcotics, the remaining number of pieces of suspicious-looking letter mail is overwhelming. Moreover, a warrant procedure need not be unduly burdensome. A Customs Inspector could each morning display to a magistrate letters from the previous day's mail that he wished to open and indicate his reasons for so wishing; conceivably, the warrant procedure could be conducted entirely orally so long as a complete record was maintained; the Government could station a magistrate on a regular full or part-time basis at such centers as the New York Post Office, where the volume of mail is heaviest. Other techniques both to facilitate examination of letters short of opening them and to streamline the warrant process might be devised.

In light of all of these seemingly feasible alternatives, we are unpersuaded by the Government's argument. Indeed, that argument is seriously compromised by the fact that, after the seizure in New York of the eight envelopes, officials at the Washington, D.C. Post Office were alerted; and when they intercepted three similar envelopes, they sought and obtained a search warrant. The course they chose to take strikes us as responsive to the Supreme Court's repeated admonitions that the warrant requirement "is not an inconvenience to be somehow `weighed' against the claims of police efficiency," Coolidge v. New Hampshire, supra, at 481, 91 S.Ct. at 2046; that the inconvenience and delay involved in obtaining a warrant are "never very convincing reasons" for failing to obtain one, Johnson v. United States, supra, at 15; that "the Constitution recognizes higher values than speed and efficiency," Stanley v. Illinois, 405 U.S. 645, 656, 92 S.Ct. 1208, 1215, 31 L.Ed.2d 551 (1972); and that

The needs of law enforcement stand in constant tension with the Constitution's protections of the individual against certain exercises of official power. It is precisely the predictability of these pressures that counsels a resolute loyalty to constitutional safeguards.

Almeida-Sanchez v. United States, supra, at 273, 93 S.Ct. at 2540.

The fact that the authorities locally in this jurisdiction observed, apparently without difficulty, the warrant requirement in like circumstances underscores the lack of cogency in appellees' suggestion that we are faced with one of those relatively few instances in which adherence to the warrant requirement is genuinely impracticable. There is no question that international letter mail presents a serious threat to effective drug law enforcement. But successful containment of that threat does not require abandonment of the Fourth Amendment.

The judgments of conviction are reversed and the cases remanded to the District Court for further proceedings consistent herewith.

It is so ordered.