Two federal law enforcement sources and one state government source confirmed the suspect's identity. The federal sources said investigators are reviewing an online writing posted days before the shooting that may speak to a motive.
The online posting was believed to be written by Crusius, the sources said, but that has not been confirmed.
El Paso Police Sgt. Robert Gomez said in a news conference Saturday one person is in police custody. He is a white male in his 20s, Gomez said. He was arrested without incident.
Police began receiving reports of an active shooter around 10 a.m. (noon ET), Gomez said in a brief news conference at the scene. Authorities were initially given multiple possible locations for the shooting, Gomez said, at a Walmart and the Cielo Vista Mall next door.
Local officials, including El Paso Mayor Dee Margo and police spokesman Sgt. Enrique Carrillo, have said there were multiple fatalities in the shooting.
At least 23 people were injured, according to spokesmen for two local hospitals.
Thirteen people were taken to the University Medical Center of El Paso, spokesman Ryan Mielke told CNN, and one of them has died.
Eleven victims were transported to the Del Sol Medical Center, hospital spokesman Victor Guerrero said. Nine of them are in critical but stable condition, he said.
Del Sol Medical Center CEO David Shimp said of those in critical condition, "Those are life-threatening situations."
This is a large crime scene, a large area," Gomez said of the crime scene. "So we are systematically going through it and making sure that anybody in the area -- number one, we're ruling out that no one is a suspect, and we're also making sure that those people that were separated or hurt are getting the care that they need."
A family reunification center has been set up at MacArthur Elementary School for families who might have been separated, Gomez said.
Multiple agencies, including the FBI and the local sheriff's department, have responded to the scene to assist El Paso authorities.
"This was a massacre," US Rep. Veronica Escobar, who represents the area, told CNN's Wolf Blitzer. Escobar has received conflicting reports on the numbers of casualties, she said, but added, "The numbers are shocking."
