The charge of material support of terrorism is the linchpin of many cases against people accused of acting as lower-level operatives for al-Qaida and other terrorist organizations. One alternative is to charge them with aiding the enemy. Prosecutors also could attempt to charge them with conspiracy, which is harder to prove because it requires evidence of knowledge and consent. The military jury acquitted Hamdan of conspiracy in 2008.

Hamdan was born in Khoreiba, Yemen, in 1968. Osama bin Laden hired him as a personal driver in Afghanistan in 1996, according to an affidavit Hamdan submitted about his work history. After his capture in Afghanistan, Hamdan arrived in Guantánamo in 2002.

He was first charged in July 2004, but a federal judge in Washington halted the trial. In June 2006, the U.S. Supreme Court ruled in Hamdan v. Rumsfeld that the war courts set up the Bush administration were unconstitutional and violated the Geneva Conventions as well as military law.

The original charges against Hamdan were dropped. The government filed new ones in May 2007, after Congress passed the Military Commissions Act and Bush signed it into law.

On Aug. 6, 2008, a military panel at Guantánamo convicted Hamdan of providing material support for terrorism. At trial, there was no evidence that Hamdan knew in advance of the 9/11 attacks, but that he had heard bin Laden discuss them afterward.

Hamdan was given credit for time served and transferred to Yemen to complete his sentence. He was released in January 2009. A father of four, he now works as a taxi driver.

Contacted in Yemen on Tuesday, Hamdan declined to comment, citing legal advice.

Rosenberg, a Miami Herald staff writer, reported from Guantánamo Bay, Cuba. Adam Baron contributed from Yemen.