On Saturday morning, David Johnson took his wife, Kathy, and granddaughter, Kaitlyn, on a fateful trip to their local Walmart.

Key points: David Johnson was one of 22 people killed in the El Paso Walmart shooting on Sunday

David Johnson was one of 22 people killed in the El Paso Walmart shooting on Sunday Mr Johnson died protecting his wife and granddaughter

Mr Johnson died protecting his wife and granddaughter Prosecutors plan to push for the death penalty for the 21-year-old shooter

They lived just a few blocks away, summer school holidays were almost at an end and nine-year-old Kaitlyn really wanted some Disney clothing she had seen in the store.

"They were checking out and I guess my dad saw the gunman," said Kaitlyn's mum, Stephanie Melendez.

"It happened so fast. He pushed them underneath the conveyor belt and was shot in the process."

The 63-year-old used his body to hide Kathy and Kaitlyn and shield them from bullets while the two played dead.

Stephanie and Krystal's father David died shielding his wife and granddaughter during the massacre. ( ABC News: Niall Lenihan )

When the mass murderer was out of sight, his wife tried to rouse him and escape.

But it was too late.

"If you're going to go out, that's a pretty dang good way," said Krystal Alvord, one of Mr Johnson's other daughters.

"[He sacrificed] himself to save his wife and granddaughter."

A family still in shock

A steady stream of visitors has brought flowers and offered condolences.

Kaitlyn, who is a bubbly, friendly child, has been in and out of doctor's appointments ever since.

Kaitlyn's mother is worried the tragedy may have long-term effects on the nine-year-old. ( Supplied: Stephanie Melendez )

She hasn't yet processed what happened, and her mother is understandably worried about the long-term impact the atrocity may have on her.

"She will remember her grandfather every day. Everything she does will be because of him," Stephanie said, choking back tears.

"I so wish I could tell him 'thank you', because she would not be here, and I would have lost my mum too. I would have lost both of them."

'The politics can wait'

While mass shootings are common in the United States, the aftermath of the El Paso massacre has been dominated by a heated, national political debate about racism in public life, white supremacy and gun control.

President Donald Trump's visit to the city, despite calls for him to stay away, is the main focus of the media today.

David's family, who say they don't have strong political views, wants that to stop.

"The politics can wait, we want to stay out of that," Krystal said.

"Right now, we need to listen to the victims' families and just learn about them."

That's part of the reason David's daughters are speaking to the ABC.

Despite their grief, they want the whole world to know their dad died a hero.

"We're so proud of him. He looked after his family until the end," Krystal said.

"That's how he'd want to be remembered."

Gun control may not be the answer, family says

When asked what they think could have prevented the atrocity, Mr Johnson's daughters are at a loss.

David recently celebrated his 63rd birthday with his family. ( Supplied: Stephanie Melendez )

They don't believe gun control would stop bad people from "doing bad things".

"Guns helped him," Stephanie said.

"But it was the man who looked into my father's eyes, who saw my nine-year-old. It was his decision to do this."

She doesn't blame the 21-year-old murderer's family either, who she believes is also grieving for a young man they'll never see again outside of a prison.

Prosecutors are planning to push for the death penalty, and Texas carries out more executions than any other US state.

"He killed many people, he deserves what he deserves," Krystal said. "No-one deserves to die but perhaps in one person's view, it's justice."

"We just want to make sure he can never do something like this again."

"We're so proud of him. He looked after his family until the end," David's family says. ( Supplied: Stephanie Melendez )

The Johnson family says it will take them a very long time to forgive the gunman and come to terms with the attack.

"We have to, eventually, in order to move on," Stephanie said. "But my daughter has years and years in front of her to deal with this.

"Right now, I just don't understand how someone could look into my nine-year-old's eyes and at a man who was just standing there with clothes and toys in his shopping cart and still pull the trigger.

"How could someone do that?"