A gunman robbed a Nassau Walmart Monday morning, getting away with a five-figure stash, a corporate spokeswoman confirmed.

Nassau police responded to a report of a robbery at the Sunrise Mall store in Massapequa and detectives continued to investigate Monday evening, a police spokesman said.

Store officials have been gathering evidence, including possible video footage, said Walmart spokeswoman Dianna Gee.

"This is an unfortunate situation," she said.

Gee declined to give additional details, but said Walmart is cooperating with the police and the store's "asset protection team" has been reviewing what happened.

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"Right now, our initial concern is to assist law enforcement as much as possible with the investigation," the spokeswoman said. "We're going to give them everything we can that might lead to an arrest in this crime."

The crime and the amount of money stolen has prompted the big-box discount chain to take another look at its procedures.

"We'll definitely be looking for improvements," Gee said, "and we'll look to see what happened here."

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Police did not release other details early Monday evening.