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The pilot whose twin-engine plane crashed into a Southern California home on Sunday, killing him and four people on the ground, was not a retired Chicago Police Department officer as authorities initially believed.

Antonio Pastini, 75, of Gardnerville, Nevada, piloted the plane that crashed into a single-family home in a residential section of Yorba Linda, California.

The Orange County Sheriff’s Office on Monday identified Pastini as a former Chicago police officer, based on a badge and ID they found on him.

On Tuesday, the sheriff's office said it had discovered that he was never a Chicago officer and that they “do not believe the credentials are legitimate.”

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“We recovered from the site what we believed were legitimate credentials from Chicago police with the name of the decedent on them,” a spokesperson for the Orange County Sheriff’s office told NBC News on Tuesday.

Chicago police confirmed to NBC News that Pastini was never a member of the force.

Pastini was born Jordan Isaacson, his daughter, Julia Ackley, told NBC Los Angeles.

"We have no record of anyone by either name ever being a police officer in Chicago," city police spokesman Anthony Gugliemi told NBC News.

Gugliemi said the ID that Pastini had on him has "never been a design ever issued by the Chicago Police Department." It appears to be "fictitiously created," he said.

Chicago police also said the metal star that Pastini had with him was reported stolen in 1978.

It remains unclear why Pastini’s small airplane, which climbed 7,800 feet and then quickly descended, crashed. Maja Smith, an investigator with the National Transportation Safety Board, told NBC News that witnesses of the crash claim they saw the plane breaking apart in the air.

Ackley said that her father owned a sushi restaurant in Nevada and a tree farm in Oregon. She described him as an experienced pilot who had flown for decades.