NEW YORK (AP) — Like most retailers, Walmart is accustomed to the everyday dealings of shoplifters. Now, it's confronting a bigger threat: active shooters.

Three days after a man opened fire at one of its stores in El Paso, Texas, and left at least 22 dead , the nation's largest retailer is faced with how to make its workers and customers feel safe.

The discounter has long dealt with violent crimes at its stores across the country, including one that took place less than a week ago in Mississippi where a disgruntled employee killed two co-workers and wounded a police officer. In early November 2017, three customers were killed at a Walmart in Colorado in a random shooting by a lone gunman.

The El Paso store shooting, however, was the deadliest in the company's history, Walmart spokesman Randy Hargrove confirmed. No workers were killed but two are recovering from injuries.

"No retailer is immune to a violent act," Hargrove said. "That's why we take training so seriously."

Robert Moraca, vice president for loss prevention at the National Retail Federation, said he's fielded lots of calls from retailers around the country over the weekend, many of whom just wanted to go over their security protocols.

"We naturally have a heightened security awareness," he said. He noted that most retailers have active shooting training programs for workers so there's not "a lot of knee jerk reactions."

Walmart launched computer-based active shooter training in 2015 for all its employees and then in 2017, it made its workers take it on a quarterly instead of annual basis. Last month, Walmart started incorporating virtual reality technology in its active shooter training.

The training focuses on three pillars: avoid the danger, keep your distance and lastly, defend.

In store locations with high crime, Walmart has off-duty policemen who patrol the parking lots. It also uses a wide variety of technology including towers that have surveillance cameras in its parking lots, Hargrove said.

But most of its efforts are focused on curbing shoplifting, including putting more unarmed greeters at the door. Hargrove noted that like with any catastrophic event, Walmart is reviewing its protocols.

Melissa Love, a 26-year-old store associate in Long Beach, California, said Walmart's active shooter training is inadequate and does not make her feel prepared. She said employees essentially watch a video and there is no chance to practice.

"It's kind of boring to be honest. It wasn't like you were going to learn anything," said Love, who has worked at Walmart for three years. "It's like, oh, we have to do this again, and nobody takes it seriously enough. You wouldn't know what to do if it actually happens."

Jesus M. Villahermosa, Jr., who leads a security consulting firm, says there's not much that retailers can do to stop the next active shooter. But he noted that retailers make the mistake of doing their active training on computers.

"You don't give people a chance to ask questions," he said.

In the end, however, he says it's not the responsibility of a retailer like Walmart to save people's lives.

"You need to have your own plan," he said. "You don't need to be paranoid; you just need to be prepared."

One Walmart employee in El Paso said she had worked for years at the store where the shooting occurred but now works at another store nearby. The employee, who spoke on condition that only her first name, Gabby, be used because the company has discouraged people from speaking publicly about the shooting, said she drove to work on the day of the shooting but spent four hours trying to cross the border back to her home in Ciudad Juarez because of heightened security.

"I am always prepared that the Lord will take me when and how he decides to, but I am afraid for the people who love me if something were to happen to me at work," she said.

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Retail Writer Alexandra Olson in New York contributed to this report.