GUANTANAMO BAY NAVAL BASE, Cuba (AP) — A Saudi facing a war crimes tribunal at Guantanamo Bay for allegedly aiding the Sept. 11 attack told interrogators that he bought plane tickets and facilitated money transfers for seven of the hijackers, a retired FBI agent said Wednesday, providing the most detailed account so far of evidence prosecutors intend to use in a case that has unfolded incrementally over nearly six years.

Mustafa Ahmed al-Hawsawi spoke to interrogators over four days in January 2004 as they showed him financial and travel records collected in the investigation into the attacks, admitting without remorse that he helped carry out the al-Qaida plot even if he didn't know exactly what was planned beforehand, the retired agent, Abigail Perkins, told the court at the U.S. base in Cuba.

"He indicated that he was a link in the chain, and oftentimes at the end of the chain would be an operation or an attack," said Perkins, who left the FBI after 22 years with the law enforcement agency and now works for the Department of Energy.

Al-Hawsawi, who was living in the United Arab Emirates in the months before the attack on Sept. 11, 2001, provided travel and financial assistance to at least seven of the 19 hijackers who flew planes into the World Trade Center, Pentagon and a field near Shanksville, Pennsylvania, Perkins said.

The defendant told interrogators that he considered it a legitimate strike aimed at punishing the U.S. for keeping troops in Saudi Arabia, backing regimes that al-Qaida opposed and supporting Israel in its conflict with the Palestinians, Perkins added.

"He indicated that he was very happy to have been able to support the brothers who carried out the attack," she said.

Her testimony came during the 26th pretrial hearing at the base in the case of five men held at Guantanamo for their alleged roles in the attack. They face trial by military commission on charges that include nearly 3,000 counts of murder in violation of the law of war, terrorism and hijacking and could get the death penalty if convicted. The case has been bogged down in pretrial litigation since their May 2012 arraignment.

Prosecutors called the retired FBI agent to establish that al-Hawsawi meets the legal definition of "alien unprivileged enemy belligerent" and can be prosecuted by a military commission under the law that set up the tribunal in 2009. In doing so, they provided a window into some of the evidence they would likely present at the actual trial, which has not yet been scheduled.

Lawyers for the 49-year-old al-Hawsawi have argued that he was, at most, a minor figure in the plot and that his case should be severed from the other four defendants or the charges dismissed outright. They also say any statements he made to Perkins were tainted by brutal treatment in CIA custody between his capture in Pakistan in March 2003 and when he was taken to Guantanamo in September 2006.

Perkins told the judge that she and the other agents who questioned al-Hawsawi gave him a modified advisory of his rights that did not include the right to have an attorney present, which was not required by Department of Defense rules under which they were operating. They had reviewed information provided by the CIA but were trying to obtain untainted statements that could be used to prosecute him by military commission, she said.

Defense attorneys were expected to cross-examine Perkins and another agent who took part in the interrogation when the hearing resumes Thursday.