Texas mall shooting updates: What police found after search warrant issued

As authorities work to determine a motive for the outlet mall shooting in Allen, Texas, one avenue investigators are exploring is whether this was an act of domestic terrorism, multiple law enforcement sources told ABC News.

The shooter wore patches or stickers on his clothing that raised suspicion he may have gravitated toward right-wing extremism, the sources said, though they added no motive has yet been established.

Federal agents were seen at a home in the Dallas area believed to be associated with the shooter, ABC Dallas affiliate station WFAA reported.

Federal investigators are already going through the suspect’s electronic devices and social media as they work to understand what led to the killing rampage, the sources said.

In addition to a rifle used in the shooting, sources said investigators recovered additional firearms in a vehicle associated with the shooter.

The Texas Rangers are the lead agency on the case with assistance from the FBI, ATF and Allen police.

Police radio dispatches from the Allen, Texas, mall shooting Saturday captured the chaotic moments as the massacre unfolded, including an officer who apparently confronted the killer, calling for backup before reporting, "I got him down."

"We got shots fired at the Allen Mall," an officer is heard saying in the radio dispatches, according to the Broadcastify, which records emergency transmissions.

A police officer was at the Allen Premium Outlets when the shooting erupted around 3:30 p.m. Saturday, raced to the gunfire and fatally shot the suspect, Allen Police Chief Brian Harvey said at a news conference on Saturday.

"We got people running," the officer on the scene radioed to a police dispatcher. "I need everybody I got."

A short time later, the officer radioed, "I got him down," referring to the gunman, who police have yet to identify.

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.