* Al Qaeda videographer was serving life term at Guantanamo
* Court: Conspiracy, other counts weren't war crimes in 2001
* Ruling casts doubts on other Guantanamo convictions (Adds quotes, details)
By Jane Sutton
MIAMI, Jan 25 (Reuters) - A U.S. appeals court on Friday overturned the Guantanamo war crimes conviction of an al Qaeda videographer, a ruling likely to lead to dismissal of conspiracy charges in the pending trial of five men accused of plotting the Sept. 11 attacks.
The U.S. Court of Appeals for the District of Columbia threw out the conviction of Yemeni prisoner Ali Hamza al Bahlul, ruling that the charges of which he was convicted - conspiracy, providing material support for terrorism and soliciting murder - were not internationally recognized as war crimes when the acts were committed.
Bahlul is serving a life sentence in the detention center at the Guantanamo Bay U.S. Naval Base in Cuba.
He acted as a publicist for Osama bin Laden's al Qaeda organization, making recruiting videos and taping the wills of some of the hijackers who slammed commercial jetliners into the World Trade Center, the Pentagon and a Pennsylvania field on Sept. 11, 2001.
The same appeals court threw out the conspiracy conviction of one of bin Laden's drivers, former Guantanamo prisoner Salim Hamdan, in October, on similar grounds.
Prosecutors had stopped defending Bahlul's conviction and the court's three-paragraph ruling said it had been vacated "based on the government's concession."
The prosecutors have also asked that conspiracy charges be dropped against the alleged mastermind of the Sept. 11 plot, Khalid Sheikh Mohammed, and four other men facing trial at Guantanamo.
Defense attorneys said the judge in that case was expected to grant the request at a pretrial hearing next week, although it had not previously been set for consideration until April.
The defendants in that case could still face the death penalty if convicted on other charges that include 2,976 counts of murder.
A Pentagon spokesman had no immediate comment.
The widely criticized Guantanamo war crimes court was established after the 2001 attacks to try foreign captives on terrorism-related charges outside the regular U.S. civilian and military courts. It has completed only seven cases, and defense attorneys said the appeals court rulings had essentially nullified five of them.
Defense lawyers have long argued that conspiracy and providing material support for terrorism were not internationally recognized as war crimes before the 2001 attacks.
Congress made them war crimes under a law that was passed in 2006 and revised in 2009, but the courts have ruled the law cannot be applied retroactively.
The other charge against Bahlul, soliciting murder, was based on a violent video he made encouraging attacks on U.S. targets. The legal precedent for that charge arose from a U.S. Civil War case that involved only U.S. citizens.
That charge also had no precedent in the international laws of war, said Bryan Broyles, deputy chief defense counsel for the Guantanamo tribunals.
"The only basis on which the United States relied was their fanciful notion of U.S. common law of war, something which doesn't actually exist," Broyles said.
James Connell, a defense lawyer for Sept. 11 defendant Ali Abdul-Aziz Ali, said the ruling highlighted the lack of neutrality in the Guantanamo court system, where the same Pentagon appointee, known as the convening authority, decides what charges will go to trial, what the maximum penalty will be and who will make up the jury pool.
"Every time we can get in front of a court with no vested interest, we win," Broyles said.
In addition to Bahlul and Hamdan, who were convicted by military juries, three other Guantanamo captives pleaded guilty to charges the appeals court has now ruled were not recognized as war crimes when committed.
Although those three waived their right to appeal by pleading guilty, defense lawyers have said they could ask to have the convictions vacated. (Editing by Peter Cooney)