Other employees pressed towels from the store’s automotive center into the hole where a bullet had pierced one man’s back. A shopper loaded wounded people into the back of his pickup truck and drove them to the paramedics who were setting up on one side of the store.

Mr. Serna, 36, said he was stocking laundry detergent when the shots started. “I heard this panicked voice say ‘Code Brown,’” he recalled. “Then it registered, and I said, ‘Everyone run, there is an active shooter.’”

Two store employees were wounded: a cashier, who was shot and underwent surgery, but whose injuries were not life threatening, and a greeter at the front entrance, whose finger was grazed by a bullet. Among the dead was the teenage son of a worker at a different Walmart in El Paso.

[The victims of the El Paso attack included a couple who had three young children.]

Employees at the Cielo Vista store say they looked out for their customers and for one another, and, in the days since the shooting, have formed an informal support network. Some have shown up to memorials in their navy blue Walmart vests. Employees at another nearby store made makeshift ribbons to attach to their uniforms. And many employees have changed their Facebook profile pictures to a Walmart logo with a black ribbon.

Doug McMillon, Walmart’s chief executive, met with the workers in El Paso this week, praising them for their bravery and offering support. Mr. McMillon has faced calls for the chain to stop selling guns in the wake of Saturday’s massacre, as well as the fatal shooting last week of two employees at a Walmart in Southaven, Miss.

Walmart no longer sells military-style rifles or handguns. But it still sells more firearms of other types than any other retailer.