The Libyan held as the suspected ringleader of the attack on the US consulate in Benghazi was driven by extremist anti-Western ideology, the Washington Post reported late Tuesday.
US prosecutors said in court documents filed late Tuesday that after the attacks in 2012 Ahmed Abu Khatallah, the only detainee in the case, and other armed men overran and looted the compound, then returned to a base to prepare an attack on a CIA annex nearby.
The attack killed US ambassador Chris Stevens and three other Americans.
It also led to a protracted political dispute in Washington. Republicans accused the administration of President Barack Obama of staging a politically motivated coverup by initially stating the attack stemmed from a spontaneous anti-US rally outside the compound, rather than a pre-meditated assault.
The administration eventually conceded it viewed the attack as an act of terrorism.
Abu Khatallah's motivation to attack the US facilities sprang from extremist anti-Western views, US official argue. "In the days before the attack, the defendant voiced concern and opposition to the presence of an American facility in Benghazi," prosecutors stated in the new court papers, the Post said.
And many of his associates in a militia called Ansar al-Sharia have been identified as being among a group of 20 or more armed men who massed outside the US mission on Sept. 11, 2012, breached the gate, entered the facility and set fire to the property, the motion states, according to the Post.
Abu Khatallah was seized by US special forces in Benghazi on June 15 this year, and charged two weeks later with conspiracy to provide material support and resources to terrorists. He has pleaded not guilty.
He was to appear Wednesday in US District Court in Washington for a detention hearing.
According to the Post, US officials say the single-charge indictment will be superseded later by one with additional charges including ones that carry the death penalty.
Evidence in the US case against Abu Khatallah includes "photographs and video from the attacks, testimony from witnesses, and evidence of the attacks' planners boasting of their involvement," the Post said, quoting a US official who has reviewed the case.