The Libyan militant now in U.S. custody expressed concern and opposition to the presence of an American compound in Benghazi in the days before the 2012 attacks there, the government said in a court filing.
Ahmed Abu Khattala on Wednesday is to appear at a detention hearing before a magistrate judge in U.S. District Court.
Khattala was motivated to participate in the violence by his extremist ideology, according to a filing Tuesday by the U.S. Attorney's Office.
Khattala is the first person to face prosecution in the Sept. 11, 2012, attack in Benghazi in which four Americans, including the U.S. ambassador to Libya, were killed.
In court papers, prosecutors explained why Khattala should remain in detention.
After U.S personnel evacuated the U.S. diplomatic mission in Benghazi, Khattala entered the compound and "supervised the exploitation from material at the scene," the government said.
Khattala then returned to a camp in Benghazi controlled by Ansar al-Shariah, where a large armed group began assembling for an attack on the U.S. compound's annex, according to the court papers.
The State Department has designated Ansar al-Shariah as a foreign terrorist organization. The Islamic extremist militia holds anti-Western views and advocates the establishment of Shariah law in Libya.
Khattala is a commander of Abu Obaida bin Jarrah Brigade, an extremist group that was absorbed into Ansar al-Shariah after the recent Libyan revolution, the court papers said.
Khattala's expected trial will take place alongside ongoing congressional and Justice Department investigations into the attack and the Obama administration's response to it shortly before the 2012 presidential election.