 -- A man suspected in the attacks two years ago on U.S. facilities in Benghazi, Libya, that killed U.S. Ambassador Chris Stevens and three other Americans entered a not guilty plea during a 10-minute hearing at federal court in Washington, D.C. today.

Ahmed Abu Khattala listened through an interpreter and raised his right hand, speaking only briefly and softly, his eyes watching the judge and nearly a dozen lawyers and government officials in Federal court on a rare Saturday session.

He was represented by a federal public defender and is scheduled to appear in court again on Wednesday.

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Khattalah came into the courtroom without handcuffs, wearing sandals, a black hoodie, black pants, a long gray beard, and somewhat disheveled gray hair.

He only spoke a few times, not in English, through translator. He said he understood the interpreter, swore to tell the truth, and stated his full name.

The magistrate judge explained to Khattalah that he is set to have a trial, where witnesses would testify in open court, and where he wouldn't have to testify against himself. The judge noted then that Khattalah has now been "advised of his constitutional rights."

Khattalah will be held until a detention hearing on July 2 at 11 a.m., at which time he will almost certainly continue to be detained. A status hearing is set for July 8 at 11 a.m. with the judge that will be presiding over the whole case.

Khattalah was captured in Libya earlier this month. He's expected to be arraigned this afternoon.

A law enforcement source told ABC News that Khattalah was flown by helicopter from a Navy ship early this morning to a location near Navy Yard in Washington, and he was then driven to the federal courthouse.

A criminal complaint filed against Khattalah earlier this year was unsealed after his arrest and accused the militant of "killing a person in the course of an action on a federal facility," providing and conspiring to provide "material support to terrorists resulting in death" and using a firearm in relation to a violent crime.

"It's important for us to send as a message to the world that when Americans are attacked, no matter how long it takes, we will find those responsible and bring them to justice," President Obama said after Khattalah's capture.

After Khattalah's capture, Pentagon Press Secretary Rear Admiral Jack Kirby told reporters that the Libyan government was notified of the operation, but declined to say exactly when. A spokesperson for the U.S. State Department said it was a "unilateral U.S. operation."

Kirby spoke to the amount of time it took the U.S. to grab Khattala.

"Terrorists go to great lengths to avoid capture and it can be a complicated process at getting them," Kirby told reporters. "You don't want to launch a complicated mission like this without all the proper information and resources in place. So what matters is not that it took a matter of time to get him, but that we got him."

U.S. officials questioned Khattalah aboard a U.S. Navy ship before he arrived in Washington D.C.

ABC News' PIERRE THOMAS, LUIS MARTINEZ and LEE FERRAN contributed to this report.