(CNN) - A shooting left one person dead and three others injured Friday evening in a Costco store in Southern California, police said.
A man is in custody after firing inside the store, Lt. Jeff Edwards of the Corona police said. His name wasn't immediately released.
The shooting stemmed from an argument inside the store, but the relationship among the victims and the alleged gunman is unclear, Edwards said.
Officers found four people "down" inside the Costco store: the suspect, the deceased and two injured people, Edwards said. The slain person was not immediately named. The alleged gunman and others were taken to hospitals, Edwards said.
An off-duty Los Angeles police officer was involved in the shooting, according to the Los Angeles police. The officer suffered minor injuries and has been released from the hospital.
"The Department has initiated an Administrative Investigation and is working with the Corona Police Department to learn more about the incident," Los Angeles police said in a statement.
The shooting was not believed to be a domestic dispute, he said. Police weren't looking for anyone else in connection with the crime, they tweeted.
'Emergency' doors wouldn't open, shoppers said
Some people were also injured trying to flee the store, Edwards said.
Naveed Navi and Rochelle Flores were shopping for items for a barbecue when gunshots rang out, they told CNN affiliate KTLA.
They heard four shots and tried to escape through emergency doors, but they wouldn't open, the pair told the station.
"It's not very fun when you're scared and you're running for your life and you're trying to open a door that says 'emergency' and they don't open," Flores told the station. "Everybody was freaking out. People were falling over each other."
She described chaos as shoppers tried to flee through the front entrance. CNN could not immediately reach Costco officials.
"Everybody's running around," Flores said. "It's scary."
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