On November 5, 2009, a mass shooting took place at Fort Hood, near Killeen, Texas. Nidal Hasan, a U.S. Army major and psychiatrist, fatally shot 13 people and injured more than 30 others. It was the deadliest mass shooting on an American military base.Hasan was shot and as a result paralyzed from the waist down. He was arraigned by a military court on July 20, 2011 and was charged with 13 counts of premeditated murder and 32 counts of attempted murder under the Uniform Code of Military Justice. His court-martial began on August 7, 2013. Due to the nature of the charges (more than one premeditated, or first-degree, murder case, in a single crime), Hasan faced either the death penalty or life in prison without parole upon conviction. Hasan was found guilty on 13 counts of premeditated murder and 32 counts of attempted premeditated murder on August 23, 2013, and was sentenced to death on August 28, 2013.Days after the shooting, reports in the media revealed that a Joint Terrorism Task Force had been aware of a series of e-mails between Hasan and the Yemen-based Imam Anwar al-Awlaki, who had been monitored by the NSA as a security threat, and that Hasan's colleagues had been aware of his increasing radicalization for several years. The failure to prevent the shootings led the Defense Department and the FBI to commission investigations, and Congress to hold hearings.

The U.S. government declined requests from survivors and family members of the slain to categorize the Fort Hood shooting as an act of terrorism, or motivated by militant Islamic religious convictions. In November 2011, a group of survivors and family members filed a lawsuit against the government for negligence in preventing the attack, and to force the government to classify the shootings as terrorism. The Pentagon argued that charging Hasan with terrorism was not possible within the military justice system and that such action could harm the military prosecutors' ability to sustain a guilty verdict against Hasan.

Nidal Malik Hasan (born September 8, 1970) is a former United States Army major convicted of killing 13 people and injuring more than 30 others in the Fort Hood mass shooting on November 5, 2009. Hasan was an Army Medical Corps psychiatrist. He admitted to the shootings at his court-martial in August 2013. A jury panel of 13 officers convicted him of 13 counts of premeditated murder, 32 counts of attempted murder, and unanimously recommended he be dismissed from the service and sentenced to death. Hasan is incarcerated at the United States Disciplinary Barracks at Fort Leavenworth in Kansas awaiting execution.

During the six years Hasan was a medical intern and resident at Walter Reed Army Medical Center, colleagues and superiors were concerned about his job performance and comments. Hasan was not married at the time, and was described as socially-isolated, stressed by his work with soldiers, and upset about their accounts of warfare. Two days before the shooting, less than a month before he was due to deploy to Afghanistan, Hasan gave away many of his belongings to a neighbor.Prior to the shooting, Hasan expressed critical views described by colleagues as "anti-American". An investigation conducted by the Federal Bureau of Investigation (FBI) concluded his e-mails with the late Imam Anwar al-Awlaki were related to his authorized professional research and he was not a threat. The FBI, Department of Defense (DoD) and U.S. Senate all conducted investigations after the shootings. The DoD classified the events as "workplace violence", pending prosecution of Hasan in a court-martial. The Senate released a report describing the mass shooting as "the worst terrorist attack on U.S. soil since September 11, 2001".The decision by the Army to not charge Hasan with terrorism is controversial.