Maj. Nidal Malik Hasan, the suspected shooter in the massacre at Fort Hood, is a psychiatrist at Darnall Army Medical Center on the base, according to records uncovered by ABC News.
Hasan, 39, did not die in the crossfire and is hospitalized, contrary to prior reports that he had been killed.
He received his medical degree from the Defense Department's F. Edward Hebert School of Medicine in Bethesda, Md., according to the records.
Several sources have said he was soon to be deployed to Iraq.
A military source was quoted by the Air Force Times as saying Hasan had recently been reassigned to Fort Hood from Walter Reed Army Medical Center in Washington. In 2009, sources tell ABC News, he completed a fellowship in Disaster and Preventative Psychiatry at the Center for Traumatic Stress there.
Military officials told the Associated Press Hasan was at Walter Reed for six years before being transferred to Ft. Hood in July.
The officials, who spoke on condition of anonymity because military records are confidential, had access to his military record and said he received a poor performance evaluation while at Walter Reed.
Hasan Born in Virginia, Never Married
Hasan appears in medical records from the Virginia Board of Medicine, and had a Maryland telephone number in an online file last updated in October.
Hasan had no prior overseas deployments, a Pentagon official told ABC News. An Army release shows he was promoted to the rank of Major in May 2009.
Hasan, born in Virginia, was single with no children. The Austin American-Statesman reported his parents were originally from Jordan.
Nader Hasan, his cousin, told ABC News Maj. Hasan has two brothers, one in the United States, the other in Jerusalem. The cousin described him as a pious lifelong Muslim.
Nadal Malik Hasan, Suspected Fort Hood Killer
He graduated from Virginia Tech University, where he earned a bachelor's degree with honors in biochemistry in 1997. At Walter Reed, he did his internship, residency and a fellowship.
His first name is spelled differently in different public records. Virginia spells it Nidal, but several Army officials told ABC News the name they had was Nadal. A record released to ABC News by the Pentagon listed him as Nidal (AbduWali) Malik Hasan.
Lt. Gen. Robert Cone, the officer in command of Fort Hood, said a shooter opened fire at a processing center for soldiers being deployed to Iraq and Afghanistan, and was killed by military personnel and police who shot back. Two other men were arrested as suspects.
Cone said all but one of the dead were members of the Army; the other was a civilian police officer employed by the Department of Defense at Ft. Hood.
The gun battle was apparently swift. Cone said the shooter used two handguns. It was unclear, the general said, whether he had a chance to reload before he was hit by return fire.
ABC News' Richard Esposito, Eric Noe, Luis Martinez and Desiree Adib contributed to this report.