The Los Angeles Police Department is gathering evidence and video footage in an administrative investigation into an off-duty officer who shot and killed a man authorities say attacked him inside a Southern California Costco Wholesale warehouse store.

Authorities remained tight-lipped Sunday, not responding to requests for comment about what provoked the Friday night confrontation and whether anyone but the officer was armed. Two others were critically injured in the shooting in Corona, which is about 40 miles east of Los Angeles.

The officer opened fire after Kenneth French, 32, of Riverside, “assaulted” him “without provocation” as the officer held his young child, Corona police said Saturday.

Bullets struck French and two of his family members, according to police. The officer was the only person who fired shots in the store, police said.

Rick Shureih, French’s cousin, told the Los Angeles Times that he was a “gentle giant” who was mentally disabled.

Shureih also identified the other two victims as French’s parents, Russell and Paola French, and said they remained in an intensive care unit Sunday. Authorities have not released their names.

French’s family is seeking an attorney, Shureih said, adding that French had the mental capacity of a teenager.

“He’s never been violent in the past,” Shureih told the Times. “He’s always been very cooperative and kept to himself.”

The LAPD will continue its internal probe as Corona police and the Riverside County district attorney’s office conduct a separate investigation into the shooting. The LAPD said Sunday it had no further information. Corona police and the district attorney’s office did not respond to requests for comment Sunday.

Los Angeles Police Commission President Steve Soboroff said Sunday it is Chief Michel Moore’s decision whether to put the officer on leave, but it remained unclear if that happened. The officer’s identity has not been released. He was treated and released at a nearby hospital and his child was not injured.

The department’s policies allow off-duty officers to carry concealed weapons as long as they are authorized for on-duty use, according to the LAPD manual.

Joseph Giacalone, a professor at the John Jay College of Criminal Justice and a retired New York City Police Department sergeant, said it’s justifiable to use deadly force even in a crowded store if the attacker has a weapon.

“If the guy pulled out a pocketknife and approaches him, game over,” Giacalone said Sunday.

Police have not said if French had any weapons or if the officer identified himself as police before firing.

Giacalone said video footage from Costco’s cameras and shoppers’ cellphones will be critical to the dual investigations.

While it’s not unusual for police to delay releasing information such as an officer’s name in a shooting for safety reasons, Giacalone said it’s important to get details out as quickly as possible.

“People start filling in the timelines for you” in the meantime, he said.

The shooting prompted a stampede of frightened shoppers, some who fled the store as others sought cover inside.

Witnesses reported seeing an argument between two people near a freezer section when shots rang out at least six times.