(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.

Read More