CORONA, Calif. – Authorities were trying Monday to learn why two small planes collided over a row of businesses, dropping a macabre shower of debris and body parts and killing someone inside an auto dealership when one of the aircraft punctured the roof.

All four people aboard the two aircraft also were killed in Sunday’s crash, on a clear crisp afternoon that seemed ideal for flying.

No one else was hurt, though wreckage fell on three car dealerships, all of which remained closed to customers as investigators combed through the debris in Corona, about 45 miles southeast of Los Angeles.

People in the area after the collision along the 91 Freeway described a horrific sight. Marisela Garay was working a few hundred yards away at Lucky Greek Burgers when she saw the planes come down.

She and some customers ran outside, where they saw blood and what looked like body parts on the ground.

“There was a lot of stuff everywhere. I was shocked, I couldn’t believe what happened,” said Garay, 17.

“There were bodies falling out of the sky,” witness Hector Hernandez told KCBS-TV. “One of them crashed into the top of a Ford Mustang, and another one fell not too far behind that one on the parking lot.”

In one of the car lots, the twisted hull of a plane rested against two vehicles.

Witnesses told authorities that one of the planes slammed into the other. One of the aircraft shattered on impact, while the other spiraled to the ground, left mostly intact.

Authorities haven’t released the planes’ origins or destinations. The crash occurred about a mile south of the Corona Municipal Airport, which doesn’t have a manned control tower.

The crash is the sixth in the area over the past 10 years.

Without the aid of air traffic controllers, pilots are supposed to use visual flight rules when there are clear conditions. Pilots are responsible for their own safety, making sure they steer clear from aircraft and other potential hazards.

Pilots can communicate by radio with one another, but not all do, Federal Aviation Administration spokesman Ian Gregor said.

The Riverside County Coroner’s Office identified the dead as Scott Gayle Lawrence, 55, of Cerritos; Paul Luther Carlson, 73, also of Cerritos; Brandon William Johnson, 24, of Costa Mesa; Anthony Joel Guzman, 20, of Hesperia; and Earl Smiddy, 58, of Moreno Valley.

Smiddy was crushed in the car dealership.

Investigators said Sunday night they would have to open up the fuselage of the planes to ensure that there were no additional victims.

One of the planes was a Cessna 172 registered to William A. Reinke of La Habra.

The second plane, a Cessna 150, is registered to Air Corona Inc., based in Dover, Del. Many plane owners register their aircraft in Delaware even if they are not based there because of the state’s low taxes.