A woman was shopping when she says the shooting began and described how people began to flee for safety.

Elaine Penicaro said in an interview that she was finishing up her shopping when she heard "popping" noises and began to realize how dire the situation was.

"We saw sparks flying like it was right in front of us. So we just ran into the Converse store. They locked the door. We all hunkered down in the back. And that's where we stayed," she said.

Penicaro said she heard the police arrive within five to 10 minutes.

A vigil will be held Sunday afternoon in the aftermath of the deadly shooting.

State Rep. Jeff Leach said that a vigil was planned for 5 p.m. at Cottonwood Creek Baptist Church. He made the announcement during a briefing Saturday evening.

"This community is home for us and our hearts are devastated and broken tonight no law enforcement official no elected official Ever imagines or plans to or hopes to speak in front of a press conference like this," Leach said.

Ken Fulk, the mayor of Allen, called the shooting a tragic day for the community and extended his sympathies. Fulk, who was elected in 2020, also pledged his support.

"Today is a tragic day for the city of Allen, our citizens, our friends and visitors who were at the Allen Premium Outlets today. We are a strong and caring community and we all want the victims and their families impacted by this tragedy to know that we will wrap our arms around you. And we are here for you," he said.

The shooter was killed at the scene, police said.

Allen Police Department Chief Brian Harvey said at a press briefing that an officer was at Allen Premium Outlets on an unrelated call when he heard gunshots and located the shooter who was then "neutralized."

"We are asking for the public's help if you are a witness," Harvey said.

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