A U.S. Federal Marshal secures the streets outside the U.S. federal court in Washington.

A Libyan militant accused of involvement in the 2012 attacks on U.S. government installations in Benghazi, Libya, has been talking to U.S. interrogators, U.S. officials familiar with the matter said.

Ahmed Abu Khatallah, captured in Libya on June 15 by a U.S. military and FBI team, has been interrogated both before and after he was advised of his right under U.S. law to remain silent, they said.

Abu Khatallah was transferred over the weekend to a federal prison in Alexandria, Virginia, from the U.S. Navy ship where he had been held since his capture, the officials said.

While aboard the USS New York, Abu Khatallah was interrogated first by a team of elite counterterrorism experts, known as the High Value Detainee Interrogation Group (HIG), without being read his “Miranda Rights”, a procedure in U.S. criminal cases under which a suspect is advised that he has the right to remain silent and to consult a lawyer.

He was later advised of his rights, the officials said. On Saturday, he was brought into federal court in Washington, where he pleaded not guilty to a terrorism conspiracy charge related to the Benghazi attack.

One of the officials familiar with the case said U.S. authorities believed Abu Khatallah led the attack. Another official said he was “not the only ringleader.”

Evidence linking Abu Khatallah to the attack includes video images, two officials said.

Abu Khatallah, in media interviews before his arrest, denied involvement in the Benghazi attacks.

The United States has not arrested any other suspects in the attack on a U.S. consular compound and CIA base in Benghazi on Sept. 11, 2012. Four Americans, including Christopher Stevens, the U.S. ambassador to Libya, were killed in the attack.

A spokesman for the U.S. Marshals Service declined to discuss where Abu Khatallah was being held, saying it was the agency’s policy not to discuss the locations of high-profile prisoners.

However, other sources said that he was being held in Alexandria in the same prison where Zacharias Moussaoui, a French citizen linked to the Sept. 11, 2001, attacks on New York and Washington, was held during proceedings against him at a nearby federal courthouse.

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