(CNN) -- The FBI is expected to question a suspect in the deadly attack on the U.S. consulate in Benghazi, Libya, "in the coming days," according to a U.S. government official with direct knowledge of the investigation.

The United States first became aware of Ali Ani al Harzi when he apparently posted details of the attack on social media while it was happening.

At the request of the United States, Turkish officials detained al Harzi when he entered that country after leaving Libya. Turkey then transferred him to Tunisia, where he is being held.

"We are very pleased the Tunisian government is working with American investigators to allow in person access to Ali Ani al Harzi. Under this arrangement the interviews will be under Tunisian supervision and consistent with their sovereignty and meets the needs of our investigative team," U.S. Senators Lindsey Graham and Saxby Chambliss said in a statement Saturday.

"Allowing American investigators in person access will make the interview more meaningful and is a welcome breakthrough in our efforts to find the perpetrators of the Benghazi Consulate attacks," they added.

U.S. Ambassador Christopher Stevens and three other Americans were killed during the September 11 assault.

According to the government official, al Harzi is not the only suspect federal agents are looking at.

"We're continuing to look at any and all leads," the official said, declining to say how many others are under investigation.

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