A federal appeals court is reconsidering the legality of the only remaining conviction of a Guantanamo Bay detainee who once served as Osama bin Laden's personal assistant and media relations secretary.

The full U.S. Court of Appeals for the District of Columbia Circuit heard arguments Tuesday after a divided three-judge appeals panel earlier ruled that the case against Ali Hamza al-Bahlul is legally flawed because conspiracy is not a recognized war crime under international law.

That June ruling could have limited the government's ability to prosecute terror suspects outside of the civilian justice system. The Obama administration successfully appealed the ruling to the full, 10-judge court.

The government argues that Congress acted lawfully in making conspiracy a crime that can be tried by the special military tribunals the George W. Bush administration created following the Sept. 11 attacks.

To help make their case, lawyers for the Justice Department have reached back for legal precedents set during some of the most turbulent periods in American history, including the tribunals held under martial law for those who conspired with John Wilkes Booth to assassinate President Abraham Lincoln.

According to the U.S. military, bin Laden personally tasked al-Bahlul, a Yemeni, with creating propaganda glorifying the al-Qaida bomb attack against the USS Cole Navy destroyer in 2000, which killed 17 American sailors. Al-Bahlul also helped prepare martyr wills for some of the Sept. 11 hijackers, though his defense lawyers contend he had no advance knowledge of their specific plans to hijack jetliners and crash them into the World Trade Center and Pentagon.

Without evidence of direct participation in attacks against the United States, defense attorney Michel Paradis argued it was unconstitutional and out of step with international law to try al-Bahlul before a military tribunal. As far as the law is concerned, Paradis suggested his client was no different than civilian defendants indicted for conspiracy in fraud or drug cases.

"This is plain vanilla, ordinary conspiracy," Paradis told the judges on Tuesday. "The crime of agreeing to a crime has to be tried by a jury."

After the Sept. 11 attacks, al-Bahlul was arrested in Pakistan and turned over to the U.S. military. Two military commissions were later convened at Guantanamo Bay to try al-Bahlul for conspiracy, but those panels were dissolved because of legal challenges in other cases.

In 2008, charges were re-issued against al-Bahlul, and a military commission convicted him of conspiracy, soliciting others to commit war crimes and providing material support to a terrorist organization. He was sentenced to life imprisonment and remains at the Guantanamo Bay detention center.

Last year, the appeals court threw out al-Bahlul's convictions for providing material support for terrorism and soliciting others to commit war crimes, leaving only the conspiracy conviction now at issue. If the appeals judges again vote to overturn that remaining conviction, the government could appeal the case to the U.S. Supreme Court.

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Follow Michael Biesecker on Twitter at https://twitter.com/mbieseck. His work can be found at http://bigstory.ap.org/content/michael-biesecker.