TRIPOLI, Libya (CNN) -- Faraj al-Shibli, who was suspected of involvement in the 2012 attack on the U.S. diplomatic compound in Benghazi, Libya, has been found dead, a Libyan source and locals in the town of Marj said.
Al-Shibli, whose name is also spelled Chalabi, was last seen being detained by a local militia in Marj two days ago, a Libyan source said.
It is unclear what happened to al-Shibli since then, but his body was found Monday in the eastern Libyan town of Marj.
Locals in Marj also confirmed that al-Shibli's body was found Monday.
The attack on the U.S. compound in September 2012 left four Americans dead, including U.S. Ambassador to Libya Chris Stevens.
The suspected mastermind of the attack, Ahmed Abu Khatallah, is in U.S. custody. Commandos captured him in June without a fight after he had been under surveillance for several days, U.S. officials said at the time.
He has pleaded not guilty to one count of providing material support to terrorists. He'll remain jailed until his trial, a federal magistrate ruled on July 2.
Several people were indicted under seal in 2013 in connection with the 2012 attack on the U.S. compound, sources told CNN at the time. Authorities have not revealed their names, and it was not immediately clear if al-Shibli was among them.
Several members of al Qaeda in the Arabian Peninsula, or AQAP, took part in the attack, a senior U.S. law enforcement official has told CNN.
Investigators learned that al-Shibli had contact with the AQAP as well as al Qaeda members in Pakistan, sources said.
Libyan authorities detained al-Shibli in March 2013 on suspicion of links to the attack, several officials said.
The FBI was able to interview him in the presence of Libyan officials, according to a Libyan source. It appears that al-Shibli was detained after returning from a trip to Pakistan, sources said.
It was not clear whether al-Shibli was present at the U.S. compound at the time of the attack.
AQAP was the first al Qaeda affiliate to comment on the Benghazi attack and released a statement saying that it was revenge for the death of Abu Yahya al-Libi, a senior al Qaeda operative, in Pakistan in June 2012. But it did not claim responsibility for the attack.
In the days before the attack, al Qaeda leader Ayman al-Zawahiri called for attacks on Americans in Libya to avenge the death of al-Libi.
CNN's Jomana Karadsheh reported from Libya; Holly Yan wrote from Atlanta. CNN's Paul Cruickshank, Tim Lister, Nic Robertson and Fran Townsend contributed to this report.
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