A man fatally shot by an off-duty Los Angeles police officer in a Southern California Costco was a nonverbal "gentle giant" with an intellectual disability, a relative said.

Corona police said the officer was holding his child while shopping Friday when he was assaulted "without provocation" by Kenneth French, 32. The officer, whose name was not released, fired, killing French and wounding French's parents, Russell and Paola.

The off-duty officer's gun was the only firearm involved in the incident, police said.

Rick Shureih told the The Press-Enterprise in Riverside that French, his cousin, had "to be pretty much monitored" and was always with his parents. Shureih said his cousin struggled with mental issues for years but had never been violent.

Shureih expressed outrage in a post on Facebook that included a picture of French and his parents.

"I’m not keeping quiet about this! People need to know!" Shureih wrote. "This is my family! These are the victims of the Costco shooting the other night."

Shureih said the public narrative described his family members as suspects and the officer as the victim. He said he was "sure this (shooting) was a misunderstanding" that needlessly escalated.

"Do they look intimidating to you? Did he really have to shoot them all?" Shureih wrote. "This is a family that was unarmed and was just grocery shopping. Truth will come out!"

'Is this another mass shooting?':Panic at Costco as off-duty cop kills man

Corona is a city of about 160,000 people, 50 miles east of Los Angeles in Riverside County. Corona police worked with the Riverside County District Attorney’s Office to evaluate the circumstances of the shooting. The LAPD launched its own investigation.

Witnesses described chaos in the store when several shots sent shoppers surging toward the exits amid fears of a mass shooting. Corona police said purses, backpacks and shopping bags abandoned by store patrons fleeing the scene could be claimed with proper identification.

Marlon Calimlim told The Press-Enterprise he has been a neighbor of the French family for four or five years. He described the couple as nice and said he could not recall French ever being aggressive.

“That’s not the monster that they were portraying him as,” Shureih said. “I’m not anti-police. We’re a pro-police family.”