(CN) - Libyan militant Ahmed Abu Khatallah, the key suspect in the 2012 attack on the U.S. Consulate in Benghazi that killed four Americans - including Ambassador Chris Stevens - pleaded not guilty Monday to additional charges filed by the Justice Department last week.
Khatallah entered the plea through his lawyer, federal public defender Michelle Peterson, in a 15-minute court session before a federal judge.
Last week, a federal grand jury in Washington slapped Khatallah, 43, with 17 new charges, some of which carry the death penalty. The investigation has been ongoing since his arrest in Libya in June.
The initial indictment included a charge of conspiracy to provide material support and resources to terrorists resulting in death, which has been carried forward to the superseding indictment. Four of the most serious new charges carry the death penalty, while the others involve long prison terms.
With the superseding indictment, Khatallah now faces charges of murdering an internationally protected person and murdering an officer and employee of the United States, aiding and abetting, several firearms and weapons charges, and malicious destruction of U.S. property, among others.
The attack killed Stevens, State Department information management officer Sean Smith and two security contractors, Tyrone Woods and Glen Doherty.
Peterson said she is waiting for the government to turn over additional material - including classified documents - that support the additional charges made by the grand jury.
Khatallah returns to court Dec. 9.
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