The wounded ranged in age from a 2-year-old child to an 82-year-old victim.
The suspect was identified by authorities as Patrick Crusius, 21, of Allen, Texas.
He was "taken into custody without incident" and without any law enforcement officers firing their weapons, according to El Paso Police Department Sgt. Robert Gomez. The alleged shooter's motives remains unknown, Gomez said.
At a news conference on Saturday night, El Paso police Chief Greg Allen said that 20 people had died and 26 more had been injured. Allen said that law enforcement officials were reviewing a manifesto posted by the alleged shooter and that the massacre was being investigated as a possible hate crime.

The majority of the victims were shot inside the Walmart, according to Gomez, which at the time contained more than 100 employees and what authorities have preliminarily estimated to be between 1,000 and 3,000 Saturday morning back-to-school shoppers.
A spokesperson for El Paso's Del Sol Medical Center said that 11 victims ranging in age from 35 to 82 were being treated at the facility. University Medical Center of El Paso received an additional 13 victims -- two of whom were children, ages 2 and 9, who were stabilized and transferred to El Paso Children's Hospital, according to officials. A hospital spokesperson said that nine patients were in critical condition and three had life-threatening injuries.
At 2 p.m. local time, the El Paso Police Department issued a tweet making an urgent request for blood donations, and directing local residents to two facilities run by Vitalent Blood Services where they could donate blood. Within three hours, photos posted to social media showed lines stretching around the block at locations accepting local blood donors.
'On a mission'
Allen, the police chief, said the first 911 call came in at 10:39 a.m. local time, and that emergency responders were on the scene at 10:45.
The shooting began in the parking lot outside the Walmart, according to an eyewitness who said she heard gunshots as she drove through the parking lot with her mother.
Shopper Vanessa Saenz described the shooter in an interview with ABC News Radio as dressed in cargo pants and a black t-shirt, wearing ear protectors and said he looked like he was "dancing."
Moments later, Saenz saw a woman a few feet away fall to the ground.
She then described seeing victims near the shooter who became cornered -- with nowhere to run -- and then watched the gunman raise a rifle, aim it at them and start firing.
"One thing I'ever never forget is when he walked walm very confidently, like he was on a mission," she later told ABC News anchor Tom Llamas in an interview for "World New Tonight."
At 12:11 p.m. local time, the El Paso Police Department had issued a tweet that said in part, "We have multi reports of multiple shooters."
article...
