SAN JUAN, Puerto Rico — In a stunning turnaround, the former chief military prosecutor at Guantanamo Bay said Thursday he would be a defense witness for the driver of Osama bin Laden.

Air Force Col. Morris Davis, who resigned in October over alleged political interference in the U.S. military tribunals, told The Associated Press he will appear at a hearing for Salim Ahmed Hamdan.

"I expect to be called as a witness ... I'm more than happy to testify," Davis said in a telephone interview from Washington. He called it "an opportunity to tell the truth."

At the April pretrial hearing inside the U.S. military base in southeast Cuba, Hamdan's defense team plans to argue that alleged political interference cited by Davis violates the Military Commissions Act, Hamdan's military lawyer, Navy Lt. Brian Mizer, told the AP.

Davis alleges, among other things, that Pentagon general counsel William Haynes said in August 2005 that any acquittals of terrorism suspects at Guantanamo would make the United States look bad, calling into question the fairness of the proceedings.

"He said 'We can't have acquittals, we've got to have convictions,'" Davis recalled.

The former chief prosecutor says the statement by Haynes, first reported this week in The Nation magazine, occurred after the general counsel compared the Guantanamo tribunals to Nuremberg and Davis says he pointed out some of those tried at the end of World War II were acquitted, giving them more credibility in the eyes of the world.

At the time, Davis says, he shrugged off the comments. But he came to view them as alarming after he was placed in a chain of command under Haynes and the prosecutor began to sense political pressure on his work.

A Pentagon spokesman, Navy Cmdr. Jeffrey Gordon, denied that Haynes made such a comment. Gordon also denied the former prosecutor's allegations of political interference, which he has repeated in newspaper opinion columns and in interviews in recent months.

If the judge rejects the motion to dismiss, Mizer said the defense will seek to remove two top officials in the military commissions system _ legal adviser Air Force Brig. Gen. Thomas Hartmann and Convening Authority Susan Crawford _ from Hamdan's case. This would likely result in further delays to a trial that has been stalled by legal challenges.

It is not clear whether the Pentagon _ which defends the commission system as fair _ will allow Davis to testify. In December, two months after he resigned as the chief prosecutor for the Guantanamo war crimes tribunals, the Defense Department barred Davis from appearing before a Senate Judiciary subcommittee.

The U.S. holds about 275 men at Guantanamo and plans to prosecute about 80 before military commissions. The Pentagon this month charged six detainees with murder and war crimes for the Sept. 11, 2001, terror attacks and said they could be executed if convicted.

Hamdan faces up to life in prison if the tribunal convicts him of conspiracy and supporting terrorism. His lawyers admit he was a driver for bin Laden, but say he had no significant role in planning or carrying out attacks against the U.S.

Davis, now head of the Air Force judiciary, said he believes "there are some very bad men at Guantanamo and some of them deserve the death penalty." But he says civilian political appointees have improperly interfered with the work of military prosecutors.

"I think the rules are fair," he said. "I think the problem is having political appointees injected into the system. They are looking for a political outcome, not justice."

He alleges, for example, that senior officials pushed for a plea bargain in March 2007 for Australian David Hicks, allowing him to serve a nine-month sentence in his homeland for aiding the Taliban.

Davis said the sentence was too lenient and was orchestrated to help Australian Prime Minister John Howard, who was under criticism domestically for his support of President Bush and U.S. policies.