FORT HOOD, TEXAS - Army investigators look for answers into the cause of Thursday's shooting rampage on a base at Fort Hood.  Officials have a suspect in custody, an army psychiatrist who is alive and in stable condition after being shot by a civilian police officer.

Officials said they believe there was a single shooter.  They had previously reported that he was killed, but they now say he is alive.

Authorities said the shooter is Major Nidal Malik Hasan, 39.  He is an American citizen of Jordanian descent.  He was working as a military psychiatrist who was about to be shipped overseas.

Investigators believe he walked into a processing center at 1:30 p.m. CT Thursday afternoon.  He opened fire at his comrades, killing13 people, wounding 30 others.

Hasan had worked at Walter Reed Medical Center.  He was transferred because of a "poor performance evaluation."

Hasan caught the attention of officials after internet postings regarding suicide bombings and other threats.  He reportedly got into arguments with other soldiers who supported the wars in Iraq and Afghanistan.  He was against it.  Hasan had never served overseas, but he was supposed to be shipped out soon.

Continue to follow WeAreCentralPA.com and WTAJ News for the latest on this investigation.