A man held in secret U.S. government confinement for nearly a decade is expected to emerge Wednesday to take a plea deal, becoming the first "high-value" Guantanamo detainee to be convicted in a war crimes tribunal.

Majid Khan, a Pakistani who graduated from a suburban Baltimore high school, agreed to plead guilty to charges that include conspiracy and murder as part of a deal that would give him no more than 25 years in prison, and possibly less, according to court documents released a day before his first hearing before a military judge at this U.S. Navy base in Cuba.

Prosecutors accused Khan of plotting with the self-proclaimed mastermind of the Sept. 11 attack, Khalid Sheikh Mohammed, to blow up fuel tanks in the U.S., to assassinate former Pakistani President Gen. Pervez Musharraf and to provide assistance to al-Qaida.

He would be the seventh Guantanamo prisoner to be convicted but in some ways the most significant. He is likely to provide significant testimony in other war crimes cases, giving momemtum to the long-stalled military tribunals, said Karen J. Greenberg, director of the Center on National Security at Fordham Law School.

"He is someone who in a variety of countries is tied to the highest levels of al-Qaida," Greenberg said. "Getting a plea from someone like this solves the problem of how to try these guys without using evidence obtained through torture."

Khan, who turned 32 on Tuesday, has been in U.S. custody since March 2003, when Pakistani forces raided his family's home in Karachi, that country's biggest city. He was turned over to the CIA and held in secret confinement overseas until he was transferred to Guantanamo along with Mohammed and other high-value detainees and held in Camp 7, a section of the prison so secret its exact location is classified.

He has not been seen in public since his capture. His only public statements were in the transcript of an April 2007 hearing at which he denied being a member of al-Qaida and said he had twice attempted suicide to protest harsh conditions of his confinement.

Family members who still live in the Baltimore area were expected to observe Wednesday's proceedings from a viewing room at Fort Meade, Maryland, their first opportunity to see him since his capture.

Details of the plea deal were not disclosed, but a sentencing document set out the broad outlines. A jury of military officers could sentence Khan to 25 to 40 years in prison, but the Convening Authority, a Pentagon legal official who oversees the tribunals, would agree not to approve a sentence exceeding 25 years.

Since the agreement was not released, any exact sentence specified under the plea deal was not yet known, and it could be less than the maximum. Also unknown was whether Khan would be required to testify against fellow prisoners such as Mohammed, who has said he planned the Sept. 11 attack on the U.S.

Al-Arabiya TV, citing unidentified sources, reported that Khan would serve about 15 years under the deal and that military authorities already eased the conditions of his confinement at Guantanamo.

His lawyers have declined comment.

Khan's actual sentencing would be postponed for four years as part of the agreement. If he did not comply with the terms of the deal, a military judge would have the option of sentencing him to any longer sentence imposed by a jury.

Khan moved to the U.S. with his family in 1996 and was granted political asylum. He graduated from Owings Mills High School in suburban Baltimore and worked several office jobs as well as at his family's gas station.

Military prosecutors say he traveled in 2002 to Pakistan, where he was introduced to Mohammed as someone who could help al-Qaida because of his familiarity with the U.S. Prosecutors say that at one point he discussed a plot to blow up underground fuel storage tanks.

Khan allegedly volunteered to assassinate Musharraf and recorded a "martyr's video," donning an explosives vest and waiting for the former Pakistani leader to show up at a mosque, according to military documents.

Prosecutors say Khan later traveled with his wife, Rabia, to Bangkok, Thailand, where he delivered $50,000 to the Southeast Asian terror group Jemaah Islamiyah, an al-Qaida affiliate, to help fund the Aug. 5, 2003, suicide bombing of the J.W. Marriott hotel in Jakarta, Indonesia. The attack killed 11 people and wounded at least 81 more.

The U.S. military holds 171 prisoners at Guantanamo, and officials have said about 35 could face war crimes charges.

"The lesson of this plea deal is that detainees who are charged with crimes are better off than detainees who aren't," said David Remes, a veteran detainee lawyer. "If you're charged, you enter a plea deal. At least you'll know you'll be released sometime, and you have some idea when. But if you're not charged, you don't know if you'll ever be released."