Ahmed Abu Khatallah remains under a watchful eye.
The Libyan militant is an alleged mastermind in the 2012 Benghazi attack on a U.S. diplomatic compound.
And for the second time after being captured on June 15, Khatallah left a Washington DC federal court under tight security.
He faces criminal charges for the attack that killed four Americans.
On Saturday, Khatallah pleaded "not guilty" to a terrorism conspiracy charge.
And on Wednesday, his attorney said prosecutors had yet to provide any evidence of Khatallah's involvement in the attacks.
It's not immediately clear when his trial would start.
But a judge has ordered him to remain in U.S. custody as he awaits it.