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.

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. The other four were in planes, with two in each aircraft.

Guzman's family told KABC-TV the young man was a student pilot aspiring to become a commercial pilot.

"He was really going somewhere with his life, and we just can't believe that he's gone," his aunt Sally Alvarez said.

Lawrence's son told the station his father, an accountant, decided to take a flight before the start of the busy tax season.

"Everybody's in shock. One day he's here, next day he's not," Brad Lawrence said.

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

Reinke told the Los Angeles Times that he knew three of the victims aboard the planes and said the pilots of both aircraft were licensed and experienced. He said they had regularly rented planes from him.

One of the victims was a commercial pilot, but both pilots were flying for leisure at the time of the crash, Reinke said.

Reinke's phone listing was not published, and attempts to reach him were not successful.

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.

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.

William Pollack, a National Transportation Safety Board investigator, confirmed to reporters Monday that the planes collided in mid air, noting paint marks that were left from one plane to the other.

The wreckage will be taken to Palmdale, where investigators will examine the planes to try and determine what happened.

"The explanation will come later," Pollack said.

Pollack said witnesses gave differing accounts on the location of the planes before impact.

One person told investigators the Cessna 150, a plane from a Corona flight school, was headed east while the other was going north. Other witnesses said one of the aircraft was headed south, Pollack said.

"We have an aircraft either landing or taking off," and the other flying parallel the runway, Pollack said.

Eyewitnesses also told authorities they heard nothing wrong with the engine. Two certified pilots were aboard the 150, while the 172 was based in Fullerton in nearby Orange County, Pollack said.

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.

Investigators will likely try to determine if there were any other pilots in the area who saw the crash or heard any transmission between the two planes, he said.

Woodrow Anselen, 52, a member of the Corona Pilots Association, called Sunday's collision a "freak accident."

"It's an extremely rare occurrence," Anselen said. "Pilots are very vigilant in giving their positions and there are rules we have to follow."

He estimated about 350 planes are kept at the airport, which has about 64,000 landings and takeoffs each year. Anselen didn't think any of the victims in the two planes were members of the 150-member pilots association.

John Elwell, who has been a pilot for 42 years, said sometimes clear days can be more challenging that those that are overcast.

"The sunlight is the biggest problem because it is in your face and it impairs your vision," Elwell said.