The LaGrands were German nationals, having been born in Germany and having moved with their mother to the United States at age 3; at no time did they become citizens of the United States. Under the Vienna Convention on Consular Relations, the United States authorities (the State of Arizona) were required to inform them of their right to receive consular assistance from the German government at the time of their arrest. The U.S. authorities failed to do so, even after they became aware that the LaGrands were German nationals. The LaGrand brothers later contacted the German consulate of their own accord, having learned of their right to consular assistance from other sources. They appealed their sentences and convictions on the grounds that they were not informed of their right to consular assistance, and that with consular assistance they might have been able to mount a better defence. The appeal was rejected by U.S. Federal Courts based on the U.S. municipal law doctrine of procedural default, which provides that issues cannot be raised in federal court appeals unless they have first been raised in state courts. Karl LaGrand was subsequently executed by the State of Arizona on February 24, 1999.
The Federal Republic of Germany then initiated legal action in the International Court of Justice against the United States regarding Walter LaGrand.
Hours before Walter LaGrand was due to be executed, Germany applied for the Court to grant provisional measures proprio motu (i.e. without a hearing and without giving the United States the opportunity to be heard), requiring the United States to prevent the execution of Walter LaGrand. The Court granted these Germany's request. Germany then initiated action in the U.S. Supreme Court for enforcement of the provisional measures. In its judgment, the U.S. Supreme Court (Federal Republic of Germany et. al. vs. United States et. al., 526 U.S. 111, per curiam) held that it lacked jurisdiction with respect to Germany's complaint against Arizona, due to the eleventh amendment of the U.S. constitution (which prohibits federal courts from hearing lawsuits of foreign states against a U.S. state). With respect to Germany's case against the United States, it held that the doctrine of procedural default was not incompatible with the Vienna Convention, and that even if procedural default did conflict with the Vienna Convention it had been pre-empted by later federal law, the Anti-Terrorism and Effective Death Penalty Act of 1996, which explicitly legislated the doctrine of procedural default (for purposes of U.S. municipal law, later Congressional legislation overrides earlier conflicting treaties).
The U.S. Solicitor-General sent a letter to the Supreme Court, as part of these proceedings, arguing that provisional measures of the International Court of Justice are not legally binding. The United States Department of State also conveyed the ICJ's provisional measure to the Governor of Arizona without comment. The Arizona clemency board recommended a stay to the Governor, on the basis of the pending ICJ case; but the Governor of Arizona ignored the recommendation and executed Walter LaGrand anyway on March 3, 1999.
Germany then modified its complaint in the case before the International Court of Justice, alleging furthermore that the U.S. violated international law by failing to implement the provisional measures. It also was forced to modify its request for remedies: previously it had sought the U.S. to grant a new trial to Walter LaGrand, but now he had been executed this was no longer possible.
In opposition to the German submissions, the United States argued that the Vienna Convention did not grant rights to individuals, only to states; the Court rejected this argument on the grounds that the U.S. interpretation contradicted the plain meaning of the Convention. The United States argued that the Vienna Convention was meant to be exercised subject to the laws of each state party, which in the case of the United States meant subject to the doctrine of procedural default; but the Court found that domestic laws could not limit the rights of the accused under the convention, but only specify the means by which those rights were to be exercised. The United States argued that Germany was seeking to turn the Court into a international court of criminal appeal; the Court rejected this argument also.
On June 27 2001 the International Court of Justice handed down its judgement, finding in favour of Germany, that provisional measures were legally binding. The binding nature of provisional measures has been a subject of great dispute in international law; the English text of the Statute of the International Court of Justice implies they are non-binding, while the French text implies that they are. Faced with a contradiction between two equally authentic texts of the Statute, the Court considered which interpretation better served the objects and purposes of the Statute, and hence found that they are binding. This was the first time in the court's history it had ruled as such.
The Court also found that the United States violated the Vienna Convention through its application of procedural default. The Court was at pains to point out that it was not passing judgement on the doctrine itself, but only its application to cases involving the Vienna Convention.