US law enforcement authorities apprehended Johvanny Aybar-Ulloa on a stateless vessel in international waters carrying packages of cocaine in violation of the Maritime Drug Law Enforcement Act (MDLEA), 46 USC §§ 70501-70508. In appealing his subsequent conviction, the defendant made a two-step argument. First, he contended that Congress's authority to criminalise and punish conduct on the high seas under the United States Constitution must be cabined by the limitations of international law on a nation's power to criminally prosecute conduct on the high seas. Second, he argued that the United States exceeded those limitations of international law by prosecuting him in this case.

In a divided opinion, a panel of this Court trained its attention exclusively on the second part of the defendant's argument: see United States v Aybar-Ulloa, 913 F 3d 47, 53-56 (1st Cir 2019) (CMI459). Relying on prior circuit precedent, the panel majority rejected that necessary part of the defendant's argument. The defendant petitioned for his appeal to be reheard en banc.

Held: The defendant's conviction is affirmed, sentence is vacated, and the case is remanded for resentencing.

Under international law governing the seas, every vessel must sail under the flag of one, and only one, State: UNCLOS, art 92. In turn, every State maintains an obligation to 'fix the conditions for the grant of its nationality to ships, for the registration of ships in its territory, and for the right to fly its flag' (art 91.1), and to 'issue to ships to which it has granted the right to fly its flag documents to that effect' (art 91.2).

This 'flag-State' system - by which all vessels are required to fly the flag of a State, and States are in turn required to approve the conditions for granting rights to fly their flag - serves several purposes. First, by subjecting vessels to the exclusive jurisdiction of the flag State, the flag-State system guarantees freedom of navigation in international waters, as States generally may not interfere with the passage on the high seas of ships lawfully flying the flag of another State: cf UNCLOS arts 87, 90. Second, the flag-State system provides clear guidance as to which State bears the primary obligation to regulate conduct occurring on vessels on the seas: cf UNCLOS art 94. Third, the flag-State system indicates which State may bear responsibility for the conduct of a ship on the seas.

International law plainly provides that a nation's warship (or law enforcement ship) may stop and board a stateless vessel on the high seas: see UNCLOS art 110.1.d. There is thus no doubt that the US could exercise jurisdiction over the stateless vessel upon which the defendant was found.

The defendant contends that, notwithstanding the foregoing, his prosecution was prohibited by other, more specific rules and undertakings governing jurisdiction and the high seas. He first points to the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances 1988, which was adopted to give effect to UNCLOS's call on States to 'cooperate in the suppression of illicit traffic in narcotic drugs' on the high seas: UNCLOS art 108. Specifically, he points out that the 1988 Convention does not explicitly address the possibility of States exercising jurisdiction over persons found engaging in drug trafficking on stateless vessels on the high seas. But it does not rule out such prosecutions either. To the contrary, at least one United Nations body has suggested that states may exercise jurisdiction under the convention over persons found engaging in illegal activities on stateless vessels, in combination with domestic sources of authority. To implement the 1988 Convention, several European states adopted the 1995 Council of Europe Convention on Illicit Traffic by Sea. That Convention provides further support for the proposition that international law welcomes prosecutions by the seizing nation of those found engaged in drug trafficking on stateless vessels: It not only allows but requires parties to prosecute persons found trafficking drugs on stateless vessels. Several other international law instruments similarly leave open the possibility of States taking law enforcement action against persons found on stateless vessels. Such instruments typically use language indicating that States may take action 'in accordance with relevant domestic and international law' after searching a stateless vessel on the high seas. Moreover, certain bilateral instruments to which the United States is a party explicitly leave open the possibility of States taking enforcement action against persons found on board stateless vessels where the evidence so warrants.

The defendant insists that UNCLOS nevertheless prohibits his prosecution. He relies on Article 110, which provides a right to visit ships suspected of being without nationality and to search those ships if suspicion of statelessness remains after checking the ship's documents. See also Aybar-Ulloa, 913 F 3d 62-63 (Torruella J dissenting in part) (arguing that the unilateral extension of domestic jurisdiction over a stateless vessel on the high seas without a nexus violates UNCLOS). But in recognising a right to visit certain ships, including a ship 'without nationality', art 110 does not prohibit the prosecution of those on board. It simply remains silent as to whether and when the visiting nation may prosecute persons found on the ship.

The defendant argues that the Court should draw a negative inference from that silence because other articles of UNCLOS do contain express grants of authority to penalise persons found on certain vessels. For example, art 105 authorises the arrest and punishment of persons found on pirate ships. Similarly, arts 99 and 109 expressly grant the power to penalise persons for engaging in slavery and unauthorized broadcasting, respectively. The Court rejects the negative inference Aybar would have us draw for two reasons.

First, and most simply, there are obvious differences between the examples given and that of a stateless vessel, undercutting any negative inference that could be drawn from the presence of express grants in some articles but not others. A ship engaged in piracy may retain its nationality: UNCLOS art 104. So there was a reason for art 105 to expressly confirm that any state can exercise universal jurisdiction to seize and prosecute individuals on such a ship - otherwise, it might have been possible to argue that only the ship's flag State would be able to seize and prosecute those individuals. Under this reading, art 105 grants no new authority. Similarly, because vessels that engage in unauthorised broadcasting can retain their nationality, an exception was needed to overcome the presumption of exclusive flag-State jurisdiction where it was desirable for impacted states to have the possibility of arresting 'person[s] or ship[s] engaged in' this activity: see art 109.4 (providing that States receiving transmissions or suffering from interference may exercise their jurisdiction to prosecute unauthorized broadcasting). Further, because slave ships also generally retain their nationality, art 99 had to expressly impinge on flag-State jurisdiction in order to declare that enslaved persons found on any ship are ipso facto free. Without these provisions - which codify limitations on the rights of flag States where their ships engage in conduct of severe concern to the international community - other states may have presumed that their hands were tied.

Not so in the case of the stateless vessel. The presumption of flag-State jurisdiction, which arguably made the express grants of authority in arts 99, 105, and 109 necessary, simply does not apply where the vessel at issue is stateless. Rather, stateless vessels are treated as subject to the exercise of authority by any nation. Accordingly, the absence of an express grant of authority to seize and prosecute persons on board a stateless vessel in art 110 does not, on its own, establish that the defendant's seizure and prosecution are prohibited by UNCLOS.

Second, the defendant's argument cannot be squared with the approach taken in the international instruments and undertakings described. If a categorical rule against the extension of domestic jurisdiction over stateless vessels could be found in UNCLOS art 110, it is unlikely that subsequent instruments mentioning stateless vessels could avoid it or that their drafters would have been unaware of it. Instead, it appears that in the decades since UNCLOS was concluded, the relevant international organisations and actors have resolved to leave the issue to the judgment of States.