If the persons responsible for the hijacking of the commercial jets and the subsequent intentional crashes into the World Trade Center and the Pentagon on September 11 can be identified and apprehended, they could face prosecution in virtually any country that obtains custody of them.

Moreover, the widely ratified Hague Convention for the Suppression of Unlawful Seizure of Aircraft makes aircraft hijacking an international criminal offense.  It applies to accomplices as well as to the hijackers themselves.  The Convention requires each contracting state to take such measures as may be necessary to establish its jurisdiction over the offense when the offense is committed on board an aircraft registered in that state, or when the aircraft lands in that state with the offender on board, or when the alleged offender is present in its territory and it does not extradite him to one of the other states just mentioned.  The offense is deemed to be extraditable under any extradition treaty in force between contracting states.

The use of the hijacked aircraft as lethal weapons, resulting in the deaths of hundreds if not thousands of persons, may be a crime against humanity under international law.  The Statute of the International Criminal Court, which is in the process of obtaining the necessary ratifications to enter into force, defines a crime against humanity as any of several listed acts “when committed as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack.”  The acts include murder and “other inhumane acts of a similar character intentionally causing great suffering, or serious injury to body or to mental or physical health.”

Even though the International Criminal Court is not yet functioning, terrorist acts amounting to crimes against humanity would be subject to prosecution in domestic criminal courts around the world.  The United States would have jurisdiction under customary international law to proscribe such terrorist acts that occur within its own borders and to prosecute the offenders under federal anti-terrorism statutes already in force.  Other countries could exercise what is known as universal jurisdiction.  This means that any country may make such terrorist acts criminal offenses under its own law, and may prosecute the offenders if they are within its custody.

The United Nations Security Council has tried in the past to facilitate the surrender of suspected terrorists for prosecution.  It has imposed sanctions on Libya to induce the surrender of suspects in the bombing of the Pan American aircraft over Lockerbie, Scotland, and on Afghanistan to induce the surrender of Osama bin Laden to the United States or any other country where he has already been indicted for alleged terrorist activities.

International law issues could arise if and when the United States or any of its allies takes counter-measures against a country suspected of harboring the persons responsible for the terrorist acts of September 11.  The issues would be particularly acute if the counter-measures are in the form of armed action.  Armed reprisals are highly questionable under the United Nations Charter (a treaty to which the United States is a party) because of its strong emphasis on peaceful resolution of disputes.  Nevertheless, article 51 of the U.N. Charter recognizes “the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.”  Thus, if the coordinated use of force to hijack and use large airliners loaded with fuel to attack the World Trade Center and the Pentagon can be classified as an armed attack against the United States, and if it is necessary to take counter-measures involving the use of armed force in order to prevent further attacks, the United States arguably could use force under article 51 until such time as the Security Council can act to maintain international peace and security.

The North Atlantic Treaty (NATO) parties, by invoking article 5 of that Treaty, have expressed their understanding that an armed attack against the United States occurred.  Article 5 requires the NATO parties to assist the attacked country in the exercise of the right of individual or collective self-defense under article 51 of the U.N. Charter, but it does not specify the action to be taken.  It does say that the action could involve the use of armed force.

If the party responsible for the attacks on the World Trade Center and the Pentagon is not the government of the country from which the terrorists operate, a question could arise whether use of armed force that causes injury to that country is lawful.  The U.N. Charter was not drafted with such situations in mind.  An argument can be made, however, that the principle of article 51 could extend to such a case if the government is knowingly harboring the terrorists.

Any use of force in self-defense would have to be roughly proportional to the use of force defended against.

About the Author: 
Frederic L. Kirgis is Law School Association Alumni Professor at Washington and Lee University School of Law. He has written a book and several articles on United Nations law, and is a member of the Board of Editors of the American Journal of International Law.