President Trump has ordered the execution of Maj. Nidal Malik Hasan by firing squad. Hasan carried out the 2009 mass shooting at Fort Hood, Texas.
The Pentagon confirmed the order on Monday. Hasan was convicted in 2013 and sentenced to death for the attack.
The shooting killed 13 people and wounded more than 30 others. It remains the deadliest mass shooting at a U.S. military base.
Hasan, a former Army psychiatrist, opened fire at the Soldier Readiness Processing Center. He was tried in a military court and received a death sentence.
The firing squad method requires five military marksmen. One rifle typically carries a blank round so no shooter knows who fired the fatal shot.
Military executions are rare in the United States. The last one occurred in 1961, when Pvt. John Bennett was hanged for rape and attempted murder.
Hasan has been held at the U.S. Disciplinary Barracks at Fort Leavenworth, Kansas. His execution date has not been announced.
Legal appeals in military death penalty cases often take years. The order may face challenges in federal courts before it proceeds.
The case has drawn renewed attention to military justice and the death penalty. The Pentagon has not released further details on the timeline.
