SAN JUAN, Puerto Rico — As a prisoner at Guantanamo, Said Ali al-Shihri said he wanted freedom so he could go home to Saudi Arabia and work at his family's furniture store.
Instead, Shihri, who was released in 2007 under the Bush administration, is now deputy leader of al-Qaida in the Arabian Peninsula, a group that has claimed responsibility for the Christmas Day attempted bomb attack on a Detroit-bound airliner.
His potential involvement in the terrorist plot has raised new opposition to releasing Guantanamo Bay inmates, complicating President Barack Obama's pledge to close the military prison in Cuba. It also highlights the challenge of identifying the hard-core militants as the administration decides what to do with the remaining 198 prisoners.
Like other former Guantanamo detainees who have rejoined al-Qaida in Yemen, Shihri, 36, won his release despite jihadist credentials such as, in his case, urban warfare training in Afghanistan.
He later goaded the United States, saying Guantanamo only strengthened his anti-American convictions.
"By God, our imprisonment has only increased our persistence and adherence to our principles," he said in a speech when al-Qaida in the Arabian Peninsula formed in Yemen in January 2009. It was included in a propaganda film for the group.
Shihri and another Saudi released from Guantanamo in 2006, Ibrahim Suleiman al-Rubaish, appear to have played significant roles in al-Qaida's expanding offshoot in Yemen. While the extent of any involvement in the airliner plot is unclear, Rubaish, 30, is a theological adviser to the group.
Overall, 14 percent of the more than 530 detainees transferred out of Guantanamo are confirmed or suspected to have been involved in terrorist activities since their release. The U.S. has repatriated 120 Saudi detainees from Guantanamo, including some still considered to pose a threat, in part because of confidence the Saudi government can minimize the risk.
Bruce Hoffman, a security studies professor at Georgetown University, stressed that the large majority of those going through the program have not rejoined extremist groups. "It's unrealistic to say none of them will return to terrorism," he said. "But … there's also a risk in imprisoning people for life."