Army Lt. Gen. Robert W. Cone, commander of 3rd Corps at Fort Hood, Texas, where the incident took place, credited police for quickly bringing down the gunman. The Army has indicated Hasan was shot multiple times, but lived and is in stable condition.

"It's a terrible tragedy. We will work through it," Cone said during a nationally-televised press conference.

Two additional soldiers had been taken into custody as possible suspects, but were released.

Hasan, assigned to Darnell Army Medical Center on Fort Hood in Killeen, Texas, treated soldiers for combat stress and was preparing to deploy to Iraq or Afghanistan, according to news reports and independent sources to dscriber. The incident occurred at a readiness center that helps troops prepare for and return from deployments to war.

Hasan graduated in 2003 from the Uniformed Services University of the Health Sciences F. Edward Herbert School of Medicine in Bethesda, Md. He then completed a psychiatry residency at Walter Reed Army Medical Center in Washington, D.C. in 2007.

Records with the Virginia Board of Medicine, where Hasan is registered, show that Hasan's license was current and that no adverse actions were ever taken against Hasan.

A news report by The Associated Press indicated that Hasan had received a poor performance evaluation, the implication being that Hasan may have been disgruntled. But that information was not verified. There have been numerous other news reports attempting to paint a clearer picture of Hasan, who was apparently troubled. Some reports, including one by The New York Times quoting Hasan's family in Virginia, indicate that Hasan was harassed by fellow soldiers because he was a Muslim. Another report indicates that Hasan did not want to deploy to the Middle East.