( CNN ) A top al Qaeda in the Arabian Peninsula leader -- who a few years ago was in a U.S. detention facility -- was among five killed in an airstrike in Yemen , the terror group said , showing the organization is vulnerable even as Yemen appears close to civil war . Ibrahim al-Rubaish died Monday night in what AQAP 's media wing , Al-Malahem Media , called a `` crusader airstrike . '' The Al-Malahem Media obituary characterized al-Rubaish as a religious scholar and combat commander . A Yemeni Defense Ministry official and two Yemeni national security officials not authorized to speak on record confirmed that al-Rubaish had been killed , but could not specify how he died . Al-Rubaish was once held by the U.S. government at its detention facility in Guantanamo Bay , Cuba . In fact , he was among a number of detainees who sued the administration of then-President George W. Bush to challenge the legality of their confinement in Gitmo . He was eventually released as part of Saudi Arabia 's program for rehabilitating jihadist terrorists , a program that U.S. Sen. Jeff Sessions , R-Alabama , characterized as `` a failure . '' In December 2009 , Sessions listed al-Rubaish among those on the virtual `` 'Who 's Who ' of al Qaeda terrorists on the Arabian peninsula ... who have either graduated or escaped from the program en route to terrorist acts . '' The United States has been active in Yemen , working closely with governments there to go after AQAP leaders like al-Rubaish . While it was not immediately clear how he died , drone strikes have killed many other members of the terrorist group . Yemen , however , has been in disarray since Houthi rebels began asserting themselves last year . The Shiite minority group even managed to take over the capital of Sanaa and , in January , force out Yemeni President Abdu Rabu Mansour Hadi -- who had been a close U.S. ally in its anti-terror fight . Hadi still claims he is Yemen 's legitimate leader , and he is working with a Saudi-led military coalition to target Houthis and supporters of former President Ali Abdullah Saleh . Meanwhile , Yemen has been awash in violence and chaos -- which in some ways has been good for groups such as AQAP . A prison break earlier this month freed 270 prisoners , including some senior AQAP figures , according to a senior Defense Ministry official , and the United States pulled the last of its special operations forces out of Yemen last month , which some say makes things easier for AQAP . CNN 's Anas Hamdan and Merieme Arif contributed to this report .
AQAP says a `` crusader airstrike '' killed Ibrahim al-Rubaish . Al-Rubaish was once detained by the United States in Guantanamo .