(CNN) -- A soldier opened fire on a military processing center at Fort Hood in Texas on Thursday, killing 12 people and wounding 30, officials at the Army base said.

The gunman also was killed in the incident, which happened around 1:30 p.m. CT, Col. Benton Danner said.

Two other soldiers who were detained have been released, but another person of interest is in custody, said Christopher Haug, chief of public affairs at Fort Hood.

The gunman, slain by emergency personnel, was identified as Maj. Nidal Malik Hasan, 39, a law enforcement source told CNN.

Licensed in Virginia, Hasan was a psychiatrist who previously worked at Walter Reed Army Medical Center but more recently was practicing at Darnall Army Medical Center at Fort Hood, according to professional records.

A federal official said Hasan is a U.S. citizen of Jordanian descent, though the source was uncertain whether he was born in the United States.