BEAVERCREEK, Ohio — A gunman opened fire Monday evening inside a Walmart in Ohio and wounded four people before killing himself -- the second shooting in 24 hours to take place at a store operated by the retail giant.

The attack at the Walmart in Beavercreek, a suburb near Dayton, injured three women and a man. Three of the victims remained in critical condition Tuesday while a fourth had non-life-threatening injuries, police said in a statement.

Walmart said it was working closely with investigators to try to determine why the shooter opened fire. His name and a motive for the attack have not yet been released.

“We’re heartbroken by what’s happened at our Beavercreek, Ohio store. This remains a developing situation, and we’re working closely with investigators on the scene,” Walmart said in a statement.

Christopher Suffron told WHIO-TV in Dayton that he was shopping with his wife when they heard five or six shots ring out. “I turned around and told her to get behind me,” he said.

Suffron said he then saw the shooter about 10 feet away and the couple ran out of the store through nearby receiving doors. As they escaped, he said he heard another five or six shots.

The shooting happened almost exactly one day after two people were shot and killed outside a Walmart in south Anchorage, Alaska. Police are still searching for a suspect in that case. The store was evacuated before closing for the day, and officers helped people reach their vehicles.

Both shootings came nearly a year after a Walmart supervisor in Chesapeake, Va., fatally shot six employees two days before Thanksgiving.

Walmart, which has police outposts in some 4,600 locations nationwide, has taken steps over the years to address gun violence. The retailer based in Bentonville, Arkansas, launched a computer-based active shooter training in 2015 that focused on three pillars: avoid the danger, keep your distance and lastly, defend.

Then in 2019, after a white gunman killed 23 people at a Walmart in El Paso, Texas, in a racist attack that targeted Hispanic shoppers, Walmart discontinued sales of certain kinds of ammunition. It also asked that customers no longer openly carry firearms in its stores. The retailer now sells only hunting rifles and related ammunition.

The store in Ohio where Monday’s shooting took place was the scene of a fatal shooting involving police almost 10 years ago. A white police officer shot 22-year-old John Crawford III after he picked up an unpackaged pellet rifle he found on a shelf in August 2014. The family of the Black man reached a settlement of $1.7 million with the city of Beavercreek. The settlement included changes in police policy.