Washington (CNN) -- Ahmed Abu Khatallah, the man the U.S. accuses of being the ringleader in the 2012 attack on the American diplomatic mission in Benghazi, Libya, pleaded not guilty Saturday during a brief appearance in federal court in Washington.
Abu Khatallah wore a dark track suit and spoke quietly in Arabic with a translator as he was charged with one count of providing material support to terrorists. A federal grand jury returned a single-count indictment Thursday.
"Now that Ahmed Abu Khatallah has arrived in the United States, he will face the full weight of our justice system," U.S. Attorney General Eric Holder said. "We will prove, beyond a reasonable doubt, the defendant's alleged role in the attack that killed four brave Americans in Benghazi."
Abu Khatallah is charged with "conspiracy to provide material support and resources to terrorists, knowing and intending that these would be used in preparation for and in carrying out a killing in the course of an attack on a federal facility, and the offense resulted in death," according to Holder's statement.
The investigation is ongoing and the Justice Department can bring additional charges, the statement said.
An earlier criminal complaint in July 2013 said the FBI believed it had evidence to charge him with murder and firing a weapon at the scene of the Benghazi attacks. Those additional charges, if formally added, could bring the death penalty.
In his court appearance, the bearded Abu Khatallah requested consular assistance from the Libyan government.
He had been interrogated aboard the USS New York after being captured earlier this month. On Saturday, he was flown by helicopter from the ship, an amphibious transport dock, to the nation's capital and driven to the federal courthouse.
Abu Khatallah was to appear before a federal judge at 3:30 p.m. Saturday, according to a tweet from the FBI. Documents on the case will be made available after the hearing.
Authorities say Abu Khatallah is among the senior leaders of Ansar al Sharia, whose members were among several militias that participated in the attacks on U.S. government facilities in Benghazi on September 11-12, 2012. The attacks killed four Americans, including U.S. Ambassador to Libya Chris Stevens.
The attacks spawned a political controversy in the United States because some Republican lawmakers claim the Obama administration tried to mislead the public about them and should have done more to prevent them. The GOP critics say they plan to make Benghazi an issue for former Secretary of State Hillary Clinton, under whose watch the attacks occurred, should she decide to run for president.
The criminal investigation led by the FBI has been extraordinarily challenging, authorities say, in part because lack of Libyan government control in the city prevented investigators from visiting the crime scene for weeks.
U.S. officials, however, say they collected surveillance video, phone eavesdropping and witness statements to bring charges against Abu Khatallah and others involved. They are charged in a criminal complaint in federal court in Washington.
Abu Khatallah became the face of the militant attack, and a top target for the U.S., after he cultivated a celebrity profile in the wake of the attacks, meeting with journalists and granting interviews. He denied to CNN's Arwa Damon that he participated in the attacks.
U.S. military commandos captured Abu Khatallah in a nighttime raid June 15-16. U.S. intelligence assets concocted a ruse to lure him to a villa where the Americans surprised him. The commandos, accompanied by several FBI agents, came ashore by boat and quickly took him away. He remained on the USS New York, undergoing questioning by a team from the FBI-led High-Value Detainee Interrogation Group, until he was taken to court on Saturday.
The extended questioning, without Abu Khatallah's being advised of his Miranda rights to remain silent, is being done under an Obama administration policy intended to allow interviews for intelligence purposes. Attorney General Eric Holder authorized lengthier pre-Miranda questioning in a memo issued in December 2010.
The memo says the extended questioning can be done in exceptional cases if investigators "conclude that continued unwarned interrogation is necessary to collect valuable and timely intelligence not related to any immediate threat."
It's a model the government has used before. In 2011, the U.S. military captured Ahmed Abdulkadir Warsame, a military commander with the Somali militant group Al-Shabaab who helped broker ties between his group and the Yemen-based al Qaeda in the Arabian Peninsula.
Warsame was questioned aboard a military ship for two months before he was read his Miranda rights. He later pleaded guilty to terrorism-related charges and spent months cooperating with investigators, providing information for other cases.