DALLAS — The man accused of killing eight people and wounding several others in a mass shooting at a suburban Dallas shopping mall was discharged from the Army in 2008 because of mental health issues and apparently had been working as a security guard, according to neighbors and an Army official.

Authorities on Monday were trying to piece together what led to the attack Saturday in Allen, which ended when police shot and killed the suspected gunman, who was identified as 33-year-old Mauricio Garcia by the Texas Department of Public Safety.

Garcia joined the Army in 2008 but was terminated three months later without completing his initial training, said U.S. Army spokeswoman Heather J. Hagan, who added that the Army doesn’t disclose the reason for any soldier’s discharge.

According to an Army official who spoke on the condition of anonymity to discuss personnel issues, though, Garcia was kicked out of the Army due to mental health issues.

Federal officials are looking into whether Garcia expressed an interest in white supremacist ideology, a law enforcement official told The Associated Press. The official cautioned that the investigation is in its early stages.

Federal agents have been reviewing social media accounts that they believe Garcia used, as well as posts that expressed interest in white supremacist and neo-Nazi views, said the official, who could not discuss details of the investigation publicly and spoke to the AP on condition of anonymity.

Garcia also had a patch on his chest when police killed him that read “RWDS,” an acronym for the phrase “Right Wing Death Squad,” which is popular among right-wing extremists and white supremacy groups, the official said.

In addition to reviewing social media posts, federal agents have interviewed family members and associates of Garcia to ask about his ideological beliefs, the official said. Investigators are also reviewing financial records, other online posts they believe Garcia made and other electronic media, according to the official.

The attack happened at Allen Premium Outlets, a sprawling outdoor shopping center about 25 miles north of downtown Dallas. At least one witness said he saw what appeared to be someone in a security guard’s uniform among the dead. Another said the suspected gunman appeared to be wearing all black.

On the Dallas block where Garcia had been living at a family home until recently, neighbors said Garcia apparently worked as a security guard and that they would sometimes see him wearing his dark-colored work uniform.

None of the neighbors knew where Garcia worked, and the company that manages the mall where the attack happened didn’t immediately reply to a Monday phone message or email seeking further information, including if Garcia had worked there.

Neighbors also said that after the attack, authorities pored over the home where Garcia had lived.

A woman who lives next door to the home said she didn’t know her neighbors well, but knew them to be “very polite, very nice people.” The woman, who would only identify herself as Julie, said Garcia was always friendly, waving and honking his horn.

Allen Police Chief Brian Harvey declined to answer questions Sunday evening, saying of the investigation, “we actually don’t have a lot.”

A law enforcement official said investigators have been searching a Dallas motel where Garcia had been staying in the runup to the attack. The official said police also found multiple weapons at the scene after Garcia was killed, including an AR-15-style rifle and a handgun.

Amid protests Monday at the Texas Capitol for stricter gun control, two Republicans sided with Democrats to advance a bill that would raise the age to buy semiautomatic rifles from 18 to 21, though the measure has little or no chance of actually becoming law.

The shooting was the latest attack to contribute to the unprecedented pace of mass killings this year in the U.S. Just over a week before, five people were fatally shot in Cleveland, Texas, after a neighbor asked a man to stop firing his weapon while a baby slept, authorities said.

This year has seen an average of about one mass killing per week, according to a database maintained by the AP and USA Today in partnership with Northeastern University.

Information about Garcia emerged as the community mourned the dead and awaited word on the seven people who were wounded. Authorities have not publicly identified those who were killed.

Medical City Healthcare said Monday it was treating six patients at three of its hospitals: Three were in critical condition, two were in fair condition and one was in good condition at a children’s hospital. Police said a seventh wounded person was taken to a different hospital.

Allen, which is home to about 105,000 people, is among the Dallas-Fort Worth area’s diverse suburbs. The area saw the largest Asian American growth rate of any major U.S. metro area, according to U.S. Census figures. Those statistics show that Allen’s population is about 19% Asian, 10% Black and 11% Hispanic.

Allen also is connected to another of Texas’ recent mass shootings. Patrick Crusius lived there in 2019 before he posted a racist screed online that warned of a “Hispanic invasion” and drove to El Paso, where he opened fire at a Walmart, killing 23. Crusius, 24, pleaded guilty to federal hate crime and weapons charges in February.