Convention Against Torture -- signed by Reagan in 1988, ratified in 1994 by Senate:
Each State Party shall ensure that all acts of torture are offences under its criminal law (Article 4) . . . . The State Party in territory under whose jurisdiction a person alleged to have committed any offence referred to in article 4 is found, shall in the cases contemplated in article 5, if it does not extradite him, submit the case to its competent authorities for the purpose of prosecution.
No exceptional circumstances whatsoever, whether a state of war or a threat or war, internal political instability or any other public emergency, may be invoked as a justification of torture. . . . An order from a superior officer or a public authority may not be invoked as a justification of torture.
Geneva Conventions, Article 146:
Each High Contracting Party shall be under the obligation to search for persons alleged to have committed, or to have ordered to be committed, such grave breaches, and shall bring such persons, regardless of their nationality, before its own courts.
Charter of the International Tribunal at Nuremberg, Article 8:
The fact that the Defendant acted pursuant to order of his Government or of a superior shall not free him from responsibility, but may be considered in mitigation of punishment if the Tribunal determines that justice so requires.
U.S. Constitution, Article VI:
[A]ll Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land.