Several news organizations, officials and lawmakers have identified the suspected Fort Hood shooter as 34-year-old Spc. Ivan Lopez. He was reportedly an active member of the U.S. military.

FILE – In this Thursday, Nov. 5, 2009, file photo, an entrance is shown to Fort Hood Army Base in Fort Hood, Texas. Fort Hood says there’s been a shooting at the Texas Army base and that there have been injuries, on Wednesday, April 2, 2014. (AP Photo/Jack Plunkett)

“The shooter, who served in Iraq in 2011, had been undergoing an assessment to determine whether he had post-traumatic stress disorder, according to Lt. Gen. Mark A. Milley, the senior officer on the base, the Associated Press reports.

He was also apparently being treated for depression and anxiety and was on medications.

Officials described the shooting as being sparked by a “soldier-on-soldier” incident and said the violent act isn’t believed to be related to terrorism, however, nothing is being ruled out.

The shooter, who is believed to have acted alone, reportedly took his own life after fatally shooting three people and injuring 16 other military members.

Milley, who declined to name the shooter until his next of kin was notified, said Wednesday the shooter in the attack at the Army base was being assessed for whether he had PTSD.

The shooter leaves behind a wife, Milley said.

A Texas congressman said the shooting happened at a medical center. Rep. Michael McCaul, chairman of the House Homeland Security Committee, also identified the suspect as Ivan Lopez.

The 2009 assault on Fort Hood was the deadliest attack on a domestic military installation in U.S. history. Thirteen people were killed and more than 30 wounded.

After the shooting began, the Army’s official Twitter feed said the post had been locked down. Hours later, all-clear sirens sounded.

The Associated Press contributed to this report.