The latest fatalities brings to 31 the number of people killed during the weekend in mass shootings in El Paso and Dayton, Ohio, that have touched off a new furor over gun violence in the United States.
Patrick Crusius, 21, has been charged with a single count of capital murder in the El Paso case, court documents show, in what is likely a legal place holder to keep him in custody while the investigation is under way.
Authorities have cited a lengthy anti-immigrant manifesto, apparently posted online by the suspect before the Saturday morning shooting in the heavily Hispanic border city, which they said was evidence the bloodshed was racially motivated.
The four-page statement uploaded to 8chan, a largely un-moderated online message board often used by extremists, called the Walmart attack "a response to the Hispanic invasion of Texas."
It also expressed support for a gunman who killed 51 people at two mosques in Christchurch, New Zealand, in March.
The El Paso killings prompted 8chan founder Frederick Brennan, in an interview with the New York Times, to call for the site to be shut down. Brennan no longer has control of the site, which is now run from the Philippines by a US Army veteran, the Times reported.
Texas Governor Greg Abbott said Saturday's rampage appeared to be a hate crime and federal prosecutors called it domestic terrorism. A Texas prosecutor said the state will seek the death penalty against Crusius if he is convicted.
US President Donald Trump said Americans "must condemn racism, bigotry and white supremacy" and blamed the internet and violent video games for fostering violence.
US gun control activists say the internet and video games cannot be blamed because they are also are popular in countries where mass shootings are virtually unknown, in part because it is harder to get a firearm.