The second-deadliest US mass shooting of the year unfolded at a shopping mall in an affluent Texas suburb, leaving eight victims dead and investigators probing whether the killer may have been driven by right-wing extremism.

Authorities have not announced a motive for why the gunman, 33-year-old Mauricio Garcia, unleashed a hailstorm of bullets Saturday at Allen Premium Outlets -- about 25 miles north of Dallas.

Garcia served in the military for a brief period but was removed due to concerns about his mental health, a law enforcement source familiar with the investigation tells CNN.

The source could not specify the branch Garcia served in or what time period. CNN has reached out to the Pentagon for comment.

Garcia, who was killed at the scene by an Allen police officer who was on a nearby call, was wearing an insignia that authorities believe may be associated with extremist groups, a senior law enforcement source familiar with the investigation told CNN.

Investigators have unearthed an extensive social media presence, including neo-Nazi and White supremacist-related posts and images that authorities believe Garcia shared online, according to the source.

The indiscriminate slaughter marks yet another mass tragedy at a public place where many Americans had felt safe -- such as schools, supermarkets, parks and Fourth of July parades.

The massacre in Allen is the second-deadliest so far this year, behind the January mass shooting in Monterey Park, California, that left 11 people dead.

Live updates: The latest on the Texas mall shooting

Across the country, the US has suffered at least 202 mass shootings within the first five months of this year, according to the Gun Violence Archive. The nonprofit and CNN define mass shootings as those in which four or more people are shot, excluding the shooter.

Among the eight killed in Allen was Aishwarya Thatikonda, who was visiting the mall with a friend, CNN affiliate WFAA reported.

Thatikonda was an engineer who lived in nearby McKinney, but her family is mourning her loss from their home in India, a family representative told WFAA. The family plans to have her body sent to India, the representative said. CNN has reached out to the consulate general of India in Houston for more information.

Christian LaCour, a 20-year-old mall security guard, was also killed in the massacre. LaCour was "a sweet, caring young man who was loved greatly by our family," his sister Brianna Smith said.

LaCour was "the kind of person who would just walk into the store and everyone in the room would light up because he was there," said Max Weiss, a mall store employee.

Witness and Army vet demands change, not thoughts and prayers

Steven Spainhouer rushed to the gruesome scene after receiving a call from his son, who works at the mall's H&M store and was hiding in a break room.

When Spainhouer arrived, he "started counting the bodies on the ground ... one, two, three, five, six, seven bodies," he told CNN.

"The first girl I walked up to ... I felt for a pulse, pulled her head to the side, and she had no face," Spainhouer told CNN affiliate KTVT.

He said one child survived after his mother shielded him from the bullets. But the mother was struck and killed.

"When I rolled the mother over, he came out," Spainhouer told KTVT. "He was covered from head to toe, like somebody had poured blood on him."

Spainhouer, a former police officer and Army veteran, said the degree of carnage at the mall was "unfathomable."

"It's tough when you see a family that's out shopping, having fun, get wiped off the face of the Earth," he told KTVT.

Now, he's calling for gun reform -- not just thoughts and prayers.

"If you don't change our gun laws, put red flag laws in place and take the high capacity weapons of the street, it's going to happen again," Spainhouer told CNN.

"If we don't do something other than giving prayers and best wishes when tragedy happens it will happen again. It could happen to you."

'You don't expect to go to the mall and lose your life'

The deadly rampage started when Garcia hot out of his car and started firing into the parking lot near the mall's H&M store, according to video obtained by CNN.

A witness video shows shoppers -- some with small children -- screaming, running and ducking behind rows of cars as bullets flew.

Geoffrey Keaton was eating at the mall's Fatburger restaurant Saturday with his daughter when they heard gunshots approaching. They were rushed to a corridor and then outside, where Keaton said he saw people down on the sidewalk.

"It was fast. It was definitely not anything that you expect or (are) prepared for," Keaton told CNN.

"You don't expect to go to the mall and lose your life."

After a police officer killed Garcia, a photo obtained by CNN shows the gunman -- clad in black and tactical gear -- lying on the ground after being shot outside the Fatburger restaurant.

In addition to an AR-15 style firearm and another weapon found with Garcia, police discovered several more weapons in his car, the law enforcement source told CNN.

Garcia had worked for at least three security companies and had undergone hours of firearms proficiency training in recent years, according to a database maintained by the Texas Department of Public Safety.

The gunman was approved to work as a security guard in Texas from April 2016 until April 2020, when his license expired, according to his profile in the Texas Online Private Security database.

Help for the grieving and ailing

GoFundMe has established a verified fundraising hub to support the families of those killed and wounded in the attack.

In addition to the eight killed victims, seven people were hospitalized as of Sunday afternoon, Allen police said:

• Three patients were in critical condition and one was in fair condition at Medical City McKinney.

• One patient was in fair condition at Medical City Children's Hospital. That child's age has not been released.

• One patient was in fair condition at Medical City Plano.

• The seventh surviving patient was treated at a different area hospital, Allen police said.

The National Disaster Distress Helpline is ready to help those impacted by the mass tragedy in Allen, according to the Substance Abuse and Mental Health Services Administration, which sponsors the hotline.

"Mass shootings can have an enormous impact on people, including survivors, first responders, eyewitnesses, and even those who watch related media reports on television," SAMHSA said.

"The Disaster Distress Helpline, at 1-800-985-5990, can provide immediate counseling to anyone who has been affected by the mass shooting at a mall in Allen."