Why Again? What We Know About Fort Hood Shootings

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Authorities are trying to piece together why another soldier opened fire at Fort Hood, Texas, killing three service members, wounding 16 others and committing suicide Wednesday — just 4½ years after 13 people died in a shooting rampage on the same base.

The investigation remained in the early stages Thursday morning, and no motive had been ruled out, said Lt. Gen. Mark Milley, Fort Hood's commanding officer.

But he made a point of saying the incident didn't initially appear to be related to terrorism.

That was important news for the Fort Hood community, which was traumatized in November 2009 when Maj. Nidal Hasan, an Army psychiatrist who said he was motivated by radical Islamist philosophies, killed 13 people and wounded 32 others just a few hundred feet away.

The base was again targeted by a Muslim soldier in July 2011, when Pfc. Naser Jason Abdo was intercepted as he finalized plans to set off a bomb at a restaurant near the base's entrance.

Milley wouldn't name Wednesday's gunman or give his rank. But here's what's known about him, according to 911 emergency transcripts and accounts from U.S. military and law enforcement officials who spoke to NBC News.

Who is the shooter?

Military officials identified the man as Ivan A. Lopez, 34, who was assigned to the 13th Sustainment Command (Expeditionary) at Fort Hood and had previously served in the Army National Guard in Puerto Rico. He was at rank E-4 — in other words, a specialist or a corporal. A caller to 911 said he was "a specialist in the unit."

Lopez had a wife and a family about whom little was immediately known. NBC Dallas-Fort Worth reported that neighbors said the wife became "hysterical" when his name was mentioned on TV, and then left with investigators.

Lopez served four months in Iraq in 2011 and was being treated for depression and anxiety pending a possible diagnosis of post-traumatic stress disorder. Milley said he wasn't wounded in action but had "self-reported" a traumatic head injury.

How did the shooting unfold?

The shootings occurred about 4 p.m. (5 p.m. ET) Wednesday. Military police and other security officers responded swiftly, and the base — one of the largest in the U.S. military, home to the Army's III Corps — was on lockdown and sealed off within 15 minutes.

Officials said the gunman opened fire in one building, got into a vehicle, continued shooting and then opened fire in another building.

A military police officer stops a car in Fort Hood, Texas, after a shooting on the Army base on Wednesday, April 2, 2014.Deborah Cannon / MCT / ZUMAPRESS.com

The all-clear didn't sound until more than four hours later as Bell County sheriff's deputies, Texas Rangers, Texas State Police, military police and agents of the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives pored over a parking lot near Carl R. Darnall Army Medical Center.

Three other service members were killed under unclear circumstances — by Lopez, according to Milley.

Sixteen more were wounded. Some were treated at Darnall; nine of the most seriously injured — three with critical wounds — were in intensive care at Scott & White Memorial Hospital in nearby Temple, where doctors described gunshot wounds to people's arms, legs, abdomens, chests and necks.

Military and law enforcement officials said Lopez, who was in uniform, apparently had a beef with another service member in the motor pool that escalated to deadly heights.

After the spree, he eventually put a .45-caliber Smith & Wesson semiautomatic pistol to his head and pulled the trigger when he was confronted by a female military police officer, they said.

Private firearms aren't allowed on base, and the gunman's weapon — which Milley said was bought in the local area recently — wasn't registered with base authorities.

The shootings opened wounds still raw from Hasan's brutal assault in 2009 and raised further questions about base security and the stress service members are subjected to.