Federal authorities are investigating whether the gunman who killed eight people including children at a Dallas shopping mall had far-right links.
The attacker, who was shot dead at the scene by a police officer, has been named as Mauricio Garcia, aged 33.
Investigators are reviewing social media to look into his ideology, the BBC’s US partner CBS news reports.
During the attack he wore a clothing patch with the letters RWDS which stands for “Right Wing Death Squad”.
This is a phrase popular among right-wing extremists and white supremacy groups.
One line of enquiry is whether he was motivated by these ideals and whether he had links to like-minded people, a law enforcement source told CBS.
The gunman used an AR-15 style rifle and wore combat gear during the shooting, with multiple rounds of ammunition found on him.
Witnesses described scenes of panic and horror when the gunman got out of his car in a mall parking lot and began firing on shoppers.
The rampage was brought to an end by a police officer who was attending a different call and happened to be nearby.
Six people were pronounced dead at the scene in the north Dallas suburbs, while two died later in hospital.
At least three injured victims remained in critical condition on Sunday.
President Joe Biden described the rampage as “the latest act of gun violence to devastate our nation”.
He confirmed that children were among those killed, saying that “too many families have empty chairs at their dinner tables”.
The president called once again on his political opponents in the Republican party to support tougher gun controls.
The Republican governor of Texas, Gregg Abbott, told Fox News Sunday his aim was to target the possession of weapons by criminals and deal with a rising mental health crisis, rather than consider wider bans.
Garcia was reportedly working as a security guard at the time of the shooting and did not have a serious criminal record.
Warning: You may find descriptions below upsetting
Footage seemed to show the suspect stepping out of his vehicle in the mall car park, and opening fire on people walking nearby without warning.
One woman working in the mall said the first she knew about the attack was a customer approaching her and warning: “You all need to close the doors.”
“I was confused. Next thing you know, we hear gunshots… all you hear is like 50, 60 gunshots,” she said.
“We kept our calm as best that we could, tried to keep our customers calm… we shut the door, everything is closed. Nobody can buy anything. We’re all hiding in the back.”
Another witness, Elaine Penicaro, said she was finishing her shopping trip when she heard “all this popping”.
“So we kind of just all just stopped. But then a second later, like pop, pop, pop, pop, pop. And we saw sparks flying like it was right in front of us,” she said. “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.”
Speaking to CBS, Steven Spainhouer described how he rushed to the scene after getting a call from his son who reported shooting. He spoke of “unfathomable carnage”.
He said at least three victims could not be saved even after he applied CPR. “The first girl I walked up to was crouched down covering her head in the bushes,” he recalled. “So I felt for a pulse, pulled her head to the side, and she had no face.”
He helped a boy who was under his mother’s dead body.
“When I rolled the mother over, he came out. I asked him if he was OK and he said, ‘My mom is hurt, my mom is hurt’. So, rather than traumatise him any more, I pulled him around the corner and sat him down.”
The boy was “covered from head to toe” in blood, Mr Spainhouer said.
