The appeal of one of Osama bin Laden's top aides ended Tuesday, as the Supreme Court declined to review whether his conviction by a military tribunal exceeded that body's authority.
Without comment, the justices turned down an appeal by Ali Hamza Ahmad Suliman al-Bahlul, a propagandist for al-Qaeda and a former media secretary for bin Laden. In 2008, he was convicted of conspiracy by a military tribunal at Guantanamo Bay in Cuba and sentenced to life in prison.
Attorneys for Bahlul claimed that the Yemeni man's conviction violated a constitutional requirement that most criminal prosecutions take place in federal courts. The charge against Bahlul was a domestic one, not a violation of international law.
The U.S. Court of Appeals for the D.C. Circuit has debated the powers of the military tribunal system since the Supreme Court ruled in 2008 that those held at Guantanamo Bay have some rights in federal courts to challenge their detention.
Constitutional and international law experts and civil rights groups had joined Bahlul's attorneys in urging the justices to take the case, saying it raised constitutional questions only the Supreme Court could answer.
But the court has steadfastly refused requests to take a case that would amplify its ruling in Boumediene v. Bush.
Bahlul, who has been held at Guantanamo Bay since 2002, was originally convicted of conspiracy to commit war crimes, solicitation of others to commit crimes and providing material support for terrorism.
Only the conspiracy charge remained, however, and the circuit court split in upholding that conviction.
Judge Brett M. Kavanaugh wrote for several other judges to say that Congress may designate military commissions to try domestic offenses typically heard by civilian courts.
"The Constitution does not give foreign nations (acting through the international law of war or otherwise) a de facto veto over Congress's determination of which war crimes may be tried by U.S. military commissions," he wrote in an opinion joined by Judges Janice Rogers Brown and Thomas B. Griffith.
Other judges, endorsing more limited legal reasoning, joined to make a six-member majority to uphold the conviction.
In a 67-page dissent, three judges said that there are "constitutionally prescribed boundaries" between military and civilian courts and that the prosecution could have instead charged Bahlul with recognized war crimes or charged him in federal court.
Judges David S. Tatel, Judith W. Rogers and Cornelia T.L. Pillard said in their dissent that even though Bahlul has admitted to serving as bin Laden's personal secretary and making al-Qaeda recruitment videos, the "challenges of the war on terror do not necessitate truncating the judicial power to make room for a new constitutional order."
A ruling against the government would have made it more difficult to prosecute low-level detainees at Guantanamo Bay.
The Supreme Court gave no reason for not accepting Bahlul v. United States, and Justice Neil M. Gorsuch took no part.
Ann E. Marimow contributed to this report.