Amid sirens and heightened security, the man who allegedly masterminded the 2012 Benghazi attack is whisked away, to an undisclosed location to await his criminal prosecution on U.S. soil.

Ahmed Abu Khatallah made his first court appearance on Saturday at a U.S. District Court in Washington, just a few blocks away from the U.S. Capitol.

He was charged with conspiracy to provide "material support to terrorists resulting in deaths," in connection with the attack that killed four Americans including Ambassador Chris Stevens.

The Libyan militia leader appeared before Magistrate Judge John Facciola.

He was unshackled and kept his hands behind him as he gave answers through an interpreter.

He pleaded not guilty to the terrorism charges.

The federal charges were filed against him in July of 2013 but were kept under court seal until this month.

Earlier in the day, Khatallah was transferred into civilian law enforcement custody from a US Navy warship.