Appellant Gerónimo Pizarro-Calderon (“Pizarro”) contends that the district court erred in refusing to suppress six block-like articles — packaged in opaque beige and brown tape — which ultimately led to his conviction for possessing cocaine with intent to distribute in violation of 21 U.S.C. § 841(a)(1) (1993). We reverse.
I
BACKGROUND
The district court adopted the findings recommended by the magistrate judge who conducted the suppression hearing. On January 8, 1993, Security Officer Gladys Martinez del Valle (“Martinez”) was screening passengers and monitoring their carry-on luggage for weapons and explosives at a security checkpoint in the Isla Verde Airport terminal. See 14 C.F.R. § 107.20 (1995) (Federal Aeronautics Administration (“FAA”) regulation mandating screening requirements for carry-on luggage), § 107.21 (banning unauthorized possession of any “explosive, incendiary, or deadly or dangerous weapons” beyond airport checkpoints). Prominent signs forewarned passengers, in English and Spanish, that their persons and carry-on luggage were subject to screening and search for weapons and explosives. Security screeners normally use x-ray machines to scan all carry-on luggage; metal detectors and hand scanners to screen passengers.
While tending the x-ray monitor, Martinez noticed a carry-on bag containing an unidentifiable dark object. She had been trained to regard such dense, nonreflective objects as possible camouflage for weapons or explosives. Upon questioning by Martinez, appellant Pizarro stated that the carry-on bag belonged to him, and the nonreflective objects inside were gift boxes containing “figurines.” Concerned that the figurines reflected no distinguishable silhouette on the x-ray monitor, Martinez asked Pizarro to open the carry-on bag. When Pizarro “sort of hesitated,” United States Department of Agriculture Inspector José Mercado, working beside Martinez, directed Pizarro to open the carry-on bag, then summoned a local law enforcement officer, Juan Avilés, to the security checkpoint. 1
Pizarro opened the carry-on bag in the presence of Martinez, Officer Avilés, and Inspector Mercado, revealing a box wrapped in Christmas paper. The box contained a layer of sanitary napkins, a layer of dark blue paper and, finally, six blocks wrapped in opaque beige and brown tape. A nineteen-year veteran of the Puerto Rico Police, Officer Avilés immediately suspected that the concealed blocks contained cocaine. Whereupon he seized the carry-on bag and its contents, then arrested and handcuffed Pizarro. 2
After placing Pizarro in an airport police-station cell, Avilés contacted the United States Drug Enforcement Administration *109 (“DEA”). Shortly thereafter, DEA agents tested the blocks by piercing their opaque wrappings; the contents tested positive for cocaine. In due course, Pizarra was indicted for possessing six kilograms of cocaine with intent to distribute, in violation of 21 U.S.C. § 841(a)(1), (b)(1)(A).
Pizarra moved to suppress the test results and the cocaine, on the ground that the warrantless searches of the carry-on bag and the containers inside it (i.e., the Christmas box and the blocks enclosed in intact, opaque wrapping) violated the Fourth Amendment to the United States Constitution. The government successfully defended the challenged DEA testing as a mere continuation of the administrative search aimed at ensuring airline security.
See United States v. Pizarro-Calderon,
II
DISCUSSION
The government must demonstrate that the warrantless DEA testing of the enclosed blocks either entailed no Fourth Amendment search or came within some recognized exception to the warrant requirement.
See, e.g., United States v. Doward,
Pizarra protests on both counts. First, he says, carry-on luggage screenings must be confined to ferreting out threats to airline security (i.e., weapons and explosives used in air piracy), whereas the customary presence of Officer Avilés at the security checkpoint permitted an inference that security concerns were a mere subterfuge for intercepting contraband posing no threat to airline security. Second, even assuming probable cause to seize the suspicious blocks, a search warrant was required before the intact, opaque packaging enclosing the blocks could be pierced to test for cocaine.
A. The Searches and Seizure at the Security Checkpoint 4
Pizarra argues that the warrantless search of the carry-on bag violated his Fourth Amendment rights, ab initio, since the customary presence of Avilés at the checkpoint subverted an otherwise lawful airline security screening into a warrantless general search for contraband (viz., cocaine) unrelated to airline security. The district court found that—
the search was conducted by a security agent at the airport, and that the local police officer was summoned to the site of the search only after the initial X-ray scan did not rule out the presence of either weapons or explosives in defendant’s luggage, requiring the presence of additional security.
Pizarro-Calderon,
Routine security searches at airport checkpoints pass constitutional muster
*110
because the compelling public interest in curbing air piracy generally outweighs their limited intrusiveness.
See, e.g., United States v. Pulido-Baquerizo,
Other contraband inadvertently discovered during a routine checkpoint search for weapons and explosives may be seized and introduced in evidence at trial even though unrelated to airline security.
See, e.g., Skipwith,
As we conclude that the government failed to demonstrate that the subsequent warrant-less search of the packaged blocks by the DEA satisfied the Fourth Amendment warrant requirement, see infra Section II.B, for present purposes we simply assume arguen-do that the carry-on bag and the Christmas box were subjected to lawful airport administrative searches.
B. The Subsequent DEA Searches of the Seized Blocks
The district court upheld the warrant-less penetration of the opaque packaging enclosing the seized blocks on the ground that the DEA tests were “not ... searches]
per se”
but merely “more thorough examination[s] of the objects which had already been lawfully seized.”
Pizarro-Calderon,
The uncontroverted evidence reveals that until the DEA agents conducted their field tests, the opaque packaging enclosing the six blocks remained intact, precluding any “plain view” of their contents such as might permit a warrantless search in the absence of exigent circumstances.
See, e.g., United States v. Miller,
*111
Although probable cause, as well as exigent circumstances, may support the war-rantless
seizure
of an enclosed opaque container,
see Texas v. Brown,
Although the government was required to show that any warrantless search was valid under an exception to the warrant requirement,
see Doward,
The litigation strategy adopted by the government seems especially remarkable considering the portentous district court opinion previously entered in the
companion
ease,
United States v. Figueroa-Cruz,
The government’s attempt to distinguish the two cases misses the mark. The carry-on bags, the gift boxes, and the blocks enclosed in opaque packaging — all were discrete closed containers. Even assuming the warrantless checkpoint searches conducted on the carry-on bags and the gift boxes were lawful, the government nevertheless failed to establish that the subsequent warrantless DEA penetration of the previously unopened blocks enclosed in opaque packaging came within any recognized exception to the warrant requirement. Consequently, their war-rantless search at the police station — after any exigency had ceased — violated the Fourth amendment.
Ill
CONCLUSION
As the government failed to shoulder its burden, by demonstrating either that its war-rantless searches of the opaque packaged blocks were permissible under the Fourth Amendment, or that the admission of the tainted evidence was harmless beyond a reasonable doubt,
see United States v. Modarressi,
The district court judgment is reversed.
Notes
. Officer Avilés was employed by the airport administration to patrol the security checkpoint area and respond to incidents encountered by screeners and inspectors, in accordance with FAA regulations requiring the presence of a local law enforcement official. See 14 C.F.R. § 107.15.
. At about the same time, Martinez noticed another nonreflective object on the x-ray monitor, similar to the one observed in Pizarro's carry-on bag. The passenger in line behind Pizarro— Ariel Figueroa-Cruz — claimed ownership of the second bag, which was found to contain two Christmas gift boxes similar to the one Pizarro had been carrying. Without opening the gift boxes, Officer Avilés placed Figueroa under arrest, and transported both suspects to the airport police station.
See United States v. Figueroa-Cruz,
. The Fourth Amendment is implicated even though airport security checkpoints are manned by nongovernmental personnel, since the FAA prescribes extensive administrative directives.
See United States v. Davis,
. The factual findings underlying a suppression ruling are reviewed for clear error.
United States v. Lewis,
. The government does not contend that the packaged blocks, once removed from the checkpoint area, were subject to warrantless search for explosives.
See Skipwith,
There is no evidence or contention that screen-ers, pursuant to practice or regulation, customarily open packages of this type or size to check for weapons or explosives,
notwithstanding the prior arrest of the passenger, and the seizure of the
*111
carry-on luggage and its contents,
based on conduct unrelated to airline security.
Cf. Nix v. Williams,
Finally, the evidence precluded a contention that the DEA testing was incident to Pizarro's arrest,
see Chimel v. California,
.
Chadwick
has been overruled only as to closed containers seized from inside an
automobile. See California v. Acevedo,
. The cases cited in the magistrate-judge’s report and recommendation are inapposite to the DEA search in the present case.
See Pizarro-Calderon, 829
F.Supp. at 516 (citing
United States v. Herzbrun,
By contrast, Avilés admitted that he delivered the blocks to the DEA for the very purpose of detecting narcotics. In these circumstances-— once the focus of the search shifted from the detection of weapons to the detection of narcotics — a warrant was required unless the ensuing search came within another recognized exception to the warrant requirement.
Cf. Jacobsen,
. Avilés conceded at the suppression hearing, and the magistrate judge later found, that the contents of the blocks could not have been "known” from their outward appearance. Thus, given the undisputed evidence that the blocks were completely enclosed in opaque packaging which had to be
pierced
even for field-testing, the government's unexplicated statement that the cocaine was in Avilés' "plain view” at the checkpoint must be premised on something more illuminating than its rose-colored perception. Nor has the government attempted to argue that the outward appearance of the blocks, or the context in which they were seized, so "clearly announce[d]” the nature of their contents that it was a "virtual certainty” that they contained cocaine.
See Arkansas v. Sanders,
Nor has the government suggested that the DEA testing should be upheld under the "inventory search” exception to the warrant requirement.
Compare, e.g., Colorado v. Bertine,
. The government apparently decided to try Figueroa-Cruz separately due to insufficient evidence that the two men were traveling in tandem.
