A former Guantánamo Bay detainee is suspected of playing a role in the 2012 Benghazi, Libya, attack, The Washington Post reported late Tuesday. 

Abu Sufian bin Qumu was released from the U.S. prison in Cuba in 2007, sent to Libya, where he was detained, and then was released in 2008, according to the newspaper. He now leads a group called Ansar al-Sharia in Darnah, Libya. 

{mosads}Unidentified officials familiar with the situation told the Post that militiamen under Qumu’s command were in Benghazi the night of the attack on Sept. 11, 2012. 

It’s unclear, however, whether they were in the city collaborating in the attack or were there coincidentally, the report says.

Regardless, the State Department is preparing to soon designate Qumu’s group in Libya as a terrorist organization.

The Post reports U.S. intelligence officials know Qumu well. He trained in the early 90s at one of Osama bin Laden’s terrorist camps and joined the Taliban’s fight against U.S. troops in Afghanistan. He was later captured in Peshawar, Pakistan, and brought to Guantánamo Bay.

Officials are also looking into whether those who killed an American schoolteacher jogging in Benghazi in December were linked to the 2012 attack.

The Benghazi attack left U.S. Ambassador Christopher Stevens and three other Americans dead.