LOS ANGELES -- A pilot killed along with four people when a small plane crashed in a Southern California neighbourhood was not a retired Chicago police officer, as initially identified, authorities said Tuesday.

The Chicago Police Department has no record of Antonio Pastini, 75, ever working in the city, department spokesman Anthony Guglielmi said in an email.

Pastini was killed Sunday when the twin-engine plane he was piloting broke up in flight shortly after takeoff and fell in pieces on the Orange County community of Yorba Linda, igniting a fire in a home where four people -- still not identified -- were killed.

Witnesses said the plane came out of the clouds in one piece and "then they saw the tail breaking off and then the wing breaking off and then something like smoke before the airplane impacted the ground," said Maja Smith, an investigator with the National Transportation Safety Board.

Those witnesses did not report an explosion while the twin-engine propeller-driven Cessna 414A was in the air, she said.

Pastini had been identified Monday as a retired Chicago officer residing in Gardnerville, Nevada, by the Orange County Sheriff's Department.

Coroner's investigators recovered credentials from Pastini after the crash that appeared to identify him as a retired Chicago officer, sheriff's spokeswoman Carrie Braun said.

Discussions with the Chicago department later determined the credentials were not legitimate, Braun said.

The identification of the pilot as Antonio Pastini was not in question.

Aircraft that break apart while flying leave "fingerprints" -- tell-tale signs -- in the metal that will allow investigators to "build a sequence of the breakup that will lead them back to where it originated," said John Cox, a former commercial pilot and crash investigator who's head of the consulting firm Safety Operating Systems.

Authorities were trying to identify the people who died in the house, describing them only as two males and two females. DNA may be required because of the condition of the bodies.

The plane came down "in multiple pieces, about four or five pieces, with a long trail of smoke," said Kyle Vanderheide, 25, who was driving when he spotted it overhead.

Shawn Winch, 49, said he was in his backyard when he heard what "sounded like a missile coming at my house." He said he saw the plane veer off and debris falling.

"It wasn't intact," he said about the plane as it came toward the neighbourhood.

Debris from the plane was strewn throughout a street. One home had broken windows.

The aircraft, which can carry up to eight people, took off from Fullerton Municipal Airport about 12 miles (19 kilometres) away.

Preliminary radar data show the plane reached about 7,800 feet (2,377 metres) and then rapidly fell, said Eliott Simpson, a National Transportation Safety Board investigator.

The main cabin of the airplane and one engine were found at the bottom of a ravine in the backyard of a house, and the other engine made a hole in the street, Simpson said.

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Associated Press journalists Amy Taxin, Amanda Lee Myers and Christopher Weber in Los Angeles contributed to this report.