The soldier allegedly behind Wednesday's deadly shooting at Fort Hood was being evaluated for post-traumatic stress disorder and had seen no combat while deployed in Iraq three years ago.

And, this week's suspected shooter also bought his gun from the same place the 2009 Fort Hood shooter got his weapon.

Army officials Thursday afternoon identified the suspected murderer as Spc. Ivan Lopez, 34, a Puerto Rican father of three who authorities say had no record of misbehavior. Wednesday's tragedy at the Texas Army base left four people dead, including the gunman, and 16 injured.

"There was no indication that he was targeting specific people," said Lt. Gen. Mark Milley, head of the Army's III Corps at Ford Hood, of Lopez. "We have very strong evidence that he had a medical history that indicated an unstable psychiatric or psychological condition."

Milley also hinted at a motive for the shooting. "There may have been a verbal altercation with another soldier or soldiers," he said."There is a strong possibility that that immediately preceded the shooting."

Army psychiatrist Nidal Hasan was convicted and sentenced to death last year in the Nov. 5, 2009, attack there on his fellow soldiers as they waited inside a crowded building in Fort Hood. It remains the deadliest domestic military attack in U.S. history-- 13 died and more than 30 were wounded.

The Bureau of Alcohol, Tobacco, Firearms and Explosives traced the gun used in Wednesday's attack to a local gun shop last night, a federal law enforcement official who is not authorized to comment publicly said. The official confirmed that the gun had been purchased at Guns Galore, the same shop that sold a weapon to Hasan.

"His records show no wounds, no involvement — direct involvement in combat," said Army Secretary John McHugh, the U.S. Army's top civilian official. "As Gen. (Mark) Milley said, no record of Purple Heart or any injury that might lead us to further investigate a battle-related TBI (traumatic brain injury) or such."

Milley said the Lopez had "self-diagnosed" a traumatic brain injury. "He was not wounded in action," Milley said.

Lopez, who was on a variety of prescribed drugs including Ambien, had not yet been diagnosed for post-traumatic stress disorder. But he was also undergoing treatment for depression, anxiety, sleep disturbance and a variety of other issues, McHugh said.

"He was seen just last month by a psychiatrist," McHugh said Thursday. "He was fully examined. And as of this morning, we had no indication on the record of that examination that there was any sign of likely violence, either to himself or to others. No suicidal ideation."

Officials had planned to continue to monitor and to treat Lopez as deemed appropriate.

Now, authorities are combing through the soldier's background but have not found any evidence that he was involved in extremist organizations.

The motive for the shooting remains a mystery. The National Counter Terrorism Center said that the attack is not linked to terrorism.

"He had a clean record in terms of his behavioral," McHugh said of the suspect. "No outstanding bad marks for any kinds of major misbehaviors that we are yet aware of."

Wednesday, Lopez allegedly used a .45-caliber Smith & Wesson handgun to carry out the attacks. Milley said the shooter walked into a building on the post and opened fire, then got into a car, fired more shots and then went to another building shooting before he was engaged by responding military police.

All those wounded and killed were military personnel.

Lopez joined National Guard in Puerto Rico in 1999. Later, he joined the Army and served one year on the Sinai Peninsula in Egypt. He was assigned to the 1st Armored Division at Fort Bliss and transferred to the 154th Transportation Company in February at Fort Hood.

The suspect was assigned to the 13th Sustainment Command (Expeditionary). It's unclear when or where he was diagnosed with mental health issues.

Melissa Earle, an associate dean at the Touro College Graduate School of Social Work in New York City, cautions against assuming the suspect had PTSD, which doesn't necessarily increase the risk of violence. Traumatic brain injury, which emerged as a major concern during the wars in Iraq and Afghanistan, is more closely tied to lack of impulse control than PTSD, she says.

Stereotyping those with PTSD as violent "could be a big setback to tens of thousands of U.S. vets with PTSD who are struggling for regular lives," Earle says.

Lopez lived off post and had recently purchased the gun used in the shooting. His wife was questioned Wednesday night. The couple are both natives of Puerto Rico.

Lopez had not been assigned to one of the Army Wounded Transition Units, military units that are set up to care for wounded, injured or ill soldiers. Those assigned to these units have case managers who help them track appointments and manage their medical treatments.

A commander who knows of a soldier with mental health issues living off base may require that servicemember to move to quarters on the post, said Army Col. Steve Warren, a Pentagon spokesman. Doing so would give the commander additional authority to deal with his or her issues, including registering weapons.

Pentagon regulations require troops who live off base to register weapons if they intend to bring them on to the installations, Warren said. Those weapons cannot be concealed and base security personnel conduct random checks to ensure compliance, he said.

"We try to do everything we can to encourage soldiers to register their personal weapons, even when they live off post," McHugh said. "We are not legally able to compel them to register weapons when they reside off post."

Soldiers who live on posts in base housing may also keep registered firearms. Soldiers in barracks must keep them in a locked arms room, Warren said.

The 2013 Defense Authorization Act requires military mental health professionals to ask troops if they own a weapon or plan to buy one. It's not yet clear if Lopez was asked about his firearms.

Mental health professionals in the military, along with commanders, have a duty to warn and protect others from potentially dangerous troops, Warren said.

However, Warren acknowledged that on a post like Fort Hood, with 40,000 soldiers, checking every vehicle is not practical.

A female soldier encountered the shooter in a parking lot, Milley said.

Lopez, dressed in combat fatigues, reached to pull out his weapon from under his jacket. The female soldier then pulled out her gun and "engaged" from about 20 feet away. He then put the gun to his head and fired.

McHugh said the investigation into the Hasan shooting revealed similar limitations in sharing of information as a soldier moves jobs and locations.

There are still difficulties in sharing information so that a commander is made aware of previous counseling or problems a soldier might have had at a previous posting, said Gen. Ray Odierno, Chief of Staff of the U.S. Army.

Contributing: Jim Michaels, Tom Vanden Brook, Ray Locker, Liz Szabo, Donna Leinwand Leger, Army Times

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