By the end of Saturday's deadly rampage, eight people were killed and at least seven others were wounded from the massacre in the affluent suburb of Allen, about 25 miles north of Dallas.
In addition to the AR-15 style weapon found near him, Garcia had at least one other weapon on him when he was fatally shot in front of the mall, the source said. Police also found multiple weapons in his car.
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CNN spoke with neighbors who witnessed FBI and police at a home of an address that matches Garcia's parents Saturday night. They arrived there about an hour after the shooting and blocked off the street for several hours, neighbors said.
Shooter removed from Army over 'mental health concerns,' suspected of 'right-wing extremist ideology'
Garcia had been living in some form of transient lodging, according to the law enforcement source. Law enforcement sources briefed on the investigation told ABC News that preliminary information developed in the probe indicates that the shooter was in the U.S. Army in 2008 and was "removed due to mental health concerns."
In addition to the insignia on the shooter's equipment that suggested a right-wing extremist ideology, investigators have found social media accounts connected to the shooter that reveal hundreds of postings and images, including writings with racially or ethnically motivated violent extremist rhetoric, neo-Nazi material and material espousing the supremacy of the white race.
None of the subject's postings analyzed to date were liked or shared by other users nor were there any public comments. The shooter's account did not contain any friends or associates that were publicly visible.
Also, investigators have determined he had no criminal history and opened fire with a semi-automatic rifle. The shooter was equipped with a ballistic vest, numerous magazines and additional handguns.
Witness video showed panicked shoppers in the parking lot of Allen Premium Outlets in Texas screaming and ducking behind rows of cars. Inside the sprawling complex, employees, shoppers and families with young children bolted and hid in storage areas or back hallways, witnesses told CNN.
The gunman was killed by an Allen Police Department officer who was at the mall on an unrelated call, police said. Investigators believe the shooter was acting alone.
A photo obtained by CNN shows what appears to be the gunman lying on the ground after being shot, with an AR-15-style firearm nearby. He is clad in black body armor and appears to have several extra magazines strapped in his chest gear.
At least nine people were rushed to trauma facilities, two of whom have since died, Allen Fire Chief Jonathan Boyd said. Of the surviving victims, three were in critical condition and undergoing surgery and four were stable as of Saturday night, he said.
A Dallas-area medical group said it treated victims as young as 5 years old.
On-duty security guard among those killed
Christian LaCour, 20, died during the shooting, his sister Brianna Smith confirmed to ABC. LaCour was an on-duty security guard at the outlet mall where the shooting occurred.
"He was a really sweet kid. I'm sad that he's gone," Brianna Smith told ABC over the phone.
Christian's mother Tracye LaCour asked ABC for privacy, and said they are praying for the families of the other victims.
Witness Kingsley Ezeh said he was walking inside the mall when people behind him suddenly began running.
"I turned around and I saw two ladies rushing towards me, and then one was like 'Someone's shooting! Someone's shooting!'" he said.
Behind the fleeing women, Ezeh said he could see a man holding his neck, which "blood (was) just dripping down."
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Ezeh huddled with others in the back of a store for about an hour before police came to get them, he said. Other witnesses reported sheltering in place for up to two hours as police cleared the scene.
Aerial video showed hundreds of shoppers, some with their hands up, weaving through police cars and ambulances as they were escorted from the scene. The footage also appears to show at least three bodies covered by sheets outside the mall.
Republican US Rep. Keith Self, whose congressional district includes Allen, said the attack could have been deadlier if not for the quick response from law enforcement.
"We owe a debt of gratitude to the first responders that ran toward the gunfire and acted swiftly to neutralize the threat," Self said.
But the carnage marked yet another massacre at a public place where Americans had long felt safe -- such as supermarkets, schools and Fourth of July parades.
It also happened in the same week a gunman opened fire in a medical facility in Atlanta, killing one woman and wounding four others.
"There are questions that are lingering that the families want answers to," Gov. Greg Abbott said, such as "'Why did this happen? Why did the gunman do this? How did this happen?' And I know that those families need an answer as quickly as possible."
'The shooting happened over and over'
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Kimberly Blakey said she and her 14-year-old daughter were among the crowd trying to flee the parking lot during the attack.
"The shooting happened over and over and over again. It was nonstop," she said.
In her haste to get away, Blakey initially drove toward the gunfire before her daughter told her to turn around. But as she drove toward the exit, she said, they became stuck behind a scrum of other cars trying to do the same.
That's when she felt her car get hit twice by gunfire.
"I told my daughter to get down," Blakey said. "She did, and I could hear her start praying."
The pair managed to get out of the parking lot and didn't stop until they got home, even though the car's flat-tire warning light had come on.
"We were on a mission to get out of there," Blakey said.
At the mall's Fatburger restaurant, employee Tiffany Gipson and customers hid in a hallway behind the restaurant.
"I've never witnessed anything like this," Gipson said. "This is very traumatic for me, and I already suffer from anxiety and seizures."
ABC News contributed to this report.
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