By Casey Tolan, Paul P. Murphy, Curt Devine, Josh Campbell and Alisha Ebrahimji, CNN/StyeMagazine.com Newswire

(CNN) -- A gunman who killed eight people at a Texas shopping mall purportedly wrote online of his support for Nazi ideology, authorities said.

Mauricio Garcia, 33, also wounded at least seven others Saturday in Allen, about 25 miles north of Dallas, authorities said. He got out of his car and started firing, ambushing employees, shoppers and families with small children, a witness' dashcam video shows.

The shooter was killed at the scene by an Allen police officer who'd been on a call nearby.

Though authorities have not announced a possible motive, new details about Garcia have emerged. Here's what we know about him:

Posts reveal obsession with Nazis, guns, mass shooters

Garcia apparently espoused support for Nazi ideology, shared images of his many firearms and posted a photo of Allen Premium Outlets on a social media website in the weeks before the massacre.

A user on the Russian social media website Odnoklassniki posted photos of several receipts and an airline ticket with Mauricio Garcia's name, along with a listed birthdate matching Garcia's. A law enforcement source said investigators believe the account belonged to Garcia.

The account also posted a screenshot from Google Maps a few weeks before the shooting showing what times of day the mall was busiest.

In the account's final missive -- a rambling post from the day of the shooting -- Garcia quoted from "South Park" and other movies and TV shows, and he alluded to his struggles with undisclosed personal problems.

"Even if I did go to a psychologist," the poster writes, "Their (sic) not going to be able to fix with whatevers wrong with me. Besides that sh*t's expensive."

There were also photos posted showing a man's shirtless torso with a large swastika tattoo over the heart. It's unclear whether the man is Garcia.

The existence of the account was first reported by the New York Times, and it was later identified by a researcher with the open source intelligence website Bellingcat.

The Odnoklassniki account, which has the username "PsycoVision 5," listed no friends or groups, suggesting Garcia may have used it like a personal diary, tweeted Aric Toler, the Bellingcat researcher who identified the account.

But the posts are publicly visible to anyone with an account on the social media site, which is also known as OK.RU.

Garcia self-identified in some posts as an "incel," a term the Anti-Defamation League defines as "heterosexual men who blame women and society for their lack of romantic success." Some posts were sexist and expressed anger toward women.

Another post expressed anger toward family members who "mocked any attempt I made to be masculine..." and "told me I was disturbed..." Another post described people making jokes or awkward comments about the poster's likelihood of committing mass murder.

Other photos posted on the account include various firearms -- some of which, the user wrote, he acquired in recent months.

An April 24 post praised the Nashville school massacre shooter who killed six people -- including three children -- in March.

Other posts espoused antisemitism and echoed the "replacement theory," the false notion a conspiracy is underway to make the US population less White. Some gunmen motivated by racism have said they were inspired by the theory.

Possible ties to extremist groups emerge

Investigators are considering whether Garcia may have been driven by right-wing extremism, a senior law enforcement source familiar with the investigation tells CNN.

A photo obtained by CNN shows Garcia -- dressed in black and tactical gear -- lying on the ground after being shot. He was wearing an insignia that authorities believe may be associated with extremist groups, the source said.

Garcia wore an RWDS patch -- a reference to Right-Wing Death Squad, the source said. 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.

Neighbors of an address matching that of Garcia's parents were shocked to learn Garcia was the shooter, they told CNN.

"I know nothing happened on our block, but it sends a chill down your spine knowing the suspect lives a few houses away," neighbor Moises Carreon said.

Garcia had been living in some form of transient lodging, according to the law enforcement source. He'd been staying in an extended-stay hotel in Dallas, The Dallas Morning News reported.

Terminated by the Army after 3 months

Garcia graduated from Bryan Adams High School in east Dallas in 2008, the Dallas Independent School District said.

He entered the Army in June of that year but was not given a specific job, called a military occupational specialty, Army spokesperson Heather Hagan told CNN. He was terminated after three months and did not complete basic training, Hagan said.

The gunman was removed due to concerns about his mental health, a law enforcement source familiar with the investigation told CNN.

Under Army regulations at the time Garcia was separated, a commander could approve separation of a service member for physical or mental health conditions that interfere with an assignment or performance of duty.

In his short time in the Army, he didn't have any deployments or awards, Hagan said.

The gunman 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 shooter 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.

As part of his work, Garcia received Level II and Level III security training: The former covers security laws in Texas; the latter, which is required for all commissioned security officers and personal protection officers in Texas, includes firearm training and the demonstration of firearm proficiency, according to Jonah Nathan, vice president of Ranger Guard, a security guard service in Texas not affiliated with Garcia's employers.

Garcia had worked as a security guard in 2015 for Dallas-based Ruiz Protective Service but resigned after a few months, said the head of the company, Hector Ruiz.

Ruiz didn't recall any interactions with Garcia, he said, noting it's not unusual for security guards to work short-term or bounce between companies.

"I don't think there was anything remarkable about this guy," he said. "As a new employee, he probably worked multiple sites. They usually just start off covering posts where people are absent or call off."