However, the court's decision may be overruled by a plea bargain that will limit the time Ibrahim Ahmed Mahmoud al-Qosi of Sudan spends in prison.
Al-Qosi pleaded guilty last month to supporting terrorism, making him only the fourth Guantanamo detainee to be convicted since the prison, which has held nearly 800 men, was opened in 2002.
The jury of 10 U.S. military officers was not told about the sentence limit in the plea agreement.
It is not yet clear where he might be held: Judge Nancy Paul, an Air Force lieutenant colonel, said Wednesday that officials would have 60 days after sentencing to determine that.
She told jurors they could sentence al-Qosi to between 12 and 15 years in prison - a range that is reportedly well above the terms of the plea bargain. She said the detainee would not receive credit for the eight years and seven months he already has spent in confinement.
Navy Capt. David Iglesias, a spokesman for military prosecutors, said the recommended sentencing range was determined in discussions between attorneys for al-Qosi and the convening authority, retired Vice Adm. Bruce MacDonald, a former Navy judge advocate general with broad powers over the system for prosecuting terror suspects.
As part of the plea agreement, the 50-year-old detainee signed a statement declaring that he followed bin Laden after the al Qaeda leader's expulsion from Sudan in 1996 and continued working for him in Afghanistan.
Al-Qosi said he learned after they occurred that al Qaeda was behind the U.S. Embassy bombings in East Africa in 1998 and the 9/11 attack on the U.S., but he was not involved in their planning.
He was arrested in Pakistan after fleeing the al Qaeda hideout at Tora Bora, Afghanistan, during the U.S.-led invasion. He was among the first prisoners taken to Guantanamo.
The only witness for the prosecution at Wednesday's sentencing hearing, al Qaeda expert Robert McFadden, testified that only the most loyal followers of bin Laden would be allowed close enough to become a cook or driver.
"Trust is the major factor," said McFadden, an agent with the Naval Criminal Investigative Service.
In a closing prosecution statement to jurors, Marine Capt. Seamus Quinn said it is the support of people like al-Qosi that make al Qaeda possible.
"It would be an insult to Mr. al-Qosi and to our intelligence to think he was nothing more than running bin Laden's kitchen," said Quinn, who urged the panel to impose a 15-year sentence.
Defense attorneys presented videotapes of interviews with al-Qosi's relatives. The man's father, Ahmed al-Qosi, said his son socialized with Christians as a youth at an Italian school and said that "our spirits would be much happier" if he is returned to Sudan.
A defense lawyer, Army Maj. Todd Pierce, said that upon repatriation al-Qosi would enter a rehabilitation program run by Sudan's intelligence service that assigns extremists to moderate mosques and employs informants to track their behavior. He said the program is 85 percent effective and none of the nine men sent back to Sudan from Guantanamo have engaged in hostilities against the United States.
Al-Qosi's lawyers said he was little more than a menial worker to al Qaeda's senior leadership.
"Do you think they pulled off these horrible attacks by blabbing about it to their cooks?" defense attorney Paul Reichler said.
Al-Qosi avoided a possible life sentence at trial by pleading guilty July 7 to one count each of providing material support for terrorism and conspiracy.
The Arabic-language news channel al Arabiya, citing two unidentified sources, reported recently that the secret agreement calls for al-Qosi to serve an additional two years at most and return to Sudan afterward.
Prosecutors have pledged to let al-Qosi serve any sentence in a communal-living section of the Guantanamo prison reserved for the most cooperative detainees. That condition sparked an internal dispute because military policy calls for convicts to be held apart from other inmates.
For now there is only one convict at Guantanamo, al Qaeda media chief Ali Hamza al-Bahlul, who was sentenced in 2008 to life in prison.
Paul, the judge, said she was troubled that authorities had not developed written guidelines for the handling of convicted detainees even though another trial is under way for Omar Khadr, a young Canadian accused of killing a U.S. soldier with a grenade in Afghanistan in 2002. Opening arguments are expected in that case Thursday.
The military trials established by the Bush administration after the 9/11 attack also yielded convictions of bin Laden driver Salim Hamdan and Australian David Hicks. Both have already served their sentences and returned home.
The U.S. Supreme Court in 2006 struck down one version of the military trials, known as commissions, before Congress and the Bush administration came up with new trial rules.
President Obama revised them further to extend more legal protections to detainees, but human rights groups say the system is still unfair and prosecutions should be held in U.S. civilian courts instead.