Ramsey (D) and Kelly commenced a heroin-by-mail enterprise. They procured heroin, which was mailed in letters from Bangkok, Thailand, and sent to various locations in the District of Columbia area for collection. Two of their West German suppliers were engaged in international narcotics trafficking during the latter part of 1973 and the early part of 1974. West German agents, pursuant to court-authorized electronic surveillance, intercepted trans-Atlantic conversations between Bailey and D during which their narcotics operation was discussed. When the Germans went to Thailand, Thai officials placed them under surveillance. Ward was observed mailing letter-sized envelopes to addresses in Washington, D.C. Bailey and Ward were arrested by Thai officials on February 2, 1974; among the items seized were eleven heroin-filled envelopes addressed to the Washington, D.C., area, and later connected with Ds. A United States customs officer in New York City, without any knowledge of the foregoing events, inspected a sack of incoming international mail from Thailand. He spotted eight envelopes that were bulky and which he believed might contain merchandise. Because the envelopes were 'rather bulky,' he suspected that the envelopes might contain merchandise or contraband rather than correspondence. The physical weight of the envelopes and their feel said there was something more than paper. The inspector opened that envelop and discovered what looked to be heroin. It was. He then opened the remaining 7 envelopes. They were closed and sent to DEA, and after obtaining a search warrant, they were again opened. The heroin was removed, and they were resealed and delivered under surveillance. After Kelly collected the envelopes from the three different addresses, rendezvoused with D, and gave D a brown paper bag, federal agents arrested both of them. The bag contained the six envelopes with heroin, $1,100 in cash, and 'cutting' material for the heroin. The next day, in executing a search upon warrant of D's residence, agents recovered two pistols. Ds moved to suppress the heroin and the two pistols. The District Court denied the motions, and after a bench trial on the stipulated record, Ds were found guilty and sentenced to imprisonment for what is in effect a term of 10 to 30 years. The Court of Appeals for the District of Columbia Circuit reversed the convictions, holding that the 'border search exception to the warrant requirement' applicable to persons, baggage, and mailed packages did not apply to the routine opening of international letter mail, and held that the Constitution requires that 'before international letter mail is opened, a showing of probable cause be made to and a warrant secured from a neutral magistrate.' The Supreme Court granted certiorari.