The FBI has provided details to the public on how they can retrieve their vehicles from the outlet mall.

Those with vehicles that were left at the mall can meet at the Allen Senior Recreation Center beginning at 5:45 p.m. local time Sunday, where they will be sent to the outlet mall, the FBI said Sunday in a press release.

The senior center will be managing the retrievals until 9:30 p.m. local time, the FBI said.

"Please drop off only one individual for vehicle retrieval," the FBI said. "Be sure to have your car keys with you."

Officials have urged the public not to go directly to Allen Premium Outlets.

Preliminary information developed during the investigation indicates the suspect was in the U.S. Army in 2008 and was "removed due to mental health concerns," law enforcement sources briefed on the probe tell ABC News.

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 suspect that reveal hundreds of postings and images, including writings with racially or ethnically motivated violent extremist rhetoric, including neo-Nazi material and material espousing the supremacy of the white race, the sources said.

None of the subject's postings analyzed to date were liked or shared by other users nor were there any public comments, according to the sources. The suspect's account did not contain any friends or associates that were publicly visible, the sources said.

Investigators have determined the suspect had no criminal history and opened fire with a semi-automatic rifle, according to the sources. The shooter was equipped with a ballistic vest, numerous magazines and additional handguns, the sources said.

-ABC News' Josh Margolin

Christian LaCour, 20, is the first victim of the shooting at the Allen Premium Outlets to be identified.

LaCour died while working as a security guard at the outlet mall, his sister said.

"He was a really sweet kid," Brianna Smith told ABC News over the phone. "I’m sad that he’s gone.”

Christian's mother, Tracye LaCour, asked for privacy, telling ABC News that they are praying for the families of the other victims.

-ABC News' Miles Cohen

The suspect in the Allen, Texas, mall mass shooting was identified Sunday as Mauricio Garcia, according to law enforcement officials briefed on the investigation.

The 33-year-old Garcia was fatally shot by a police officer who rushed to the gunfire and confronted him at the outlet mall on Saturday afternoon, police said.

The Texas Department of Public Safety, which is leading the investigation, was searching Mauricio's home and vehicle on Sunday. The agency declined to comment further on Garcia and said the motive for the shooting remains under investigation.

President Joe Biden said the assailant was dressed in tactical gear and armed with an AR-15-style assault weapon he used to gun down eight people and injure at least nine others.

A memorial outside the Allen Premium Outlets continues to grow.

Dallas native Roberto Marquez has made it his life’s work to create memorials at the scene of tragedies. He told ABC News that this memorial in Allen is his 11th.

Marquez said Home Depot donated the lumber he used to build the crosses.

Volunteers from Lutheran Church Charities have also arrived at the scene with therapy dogs. The group has over 140 dogs in at least 25 states.

The same dogs in Allen on Monday were on the scene in Uvalde last year when 19 students and two teachers were killed in a mass shooting at Robb Elementary school.

A vigil for the Allen victims is set for Wednesday at 7 p.m., according to community leaders.

-ABC News' Ike Ejiochi and Abigal Shalawylo