BREAKING NEWS: Autopsies have determined the official causes of death for Paul Walker.

(CNN) -- Autopsies on Paul Walker and Roger Rodas have corroborated what many people believed: Rodas was the driver in the crash; Walker was the passenger.

Walker died of the "combined effects of traumatic and thermal injuries," the Los Angeles county coroner's office said Wednesday. The determination means the impact and the resulting heat and fire caused his death.

Rodas died of "multiple traumatic injuries," the coroner's report said.

The crash was an accident, the coroner's office said, and toxicology results could take six to eight weeks.

The autopsies were completed Tuesday, but investigators had placed a "security hold" on the results. The coroner's office did not give a reason for the secrecy.

Production of Walker's latest movie will be shut down "for a period of time," the studio said Wednesday.

"At this time we feel it is our responsibility to shut down production on 'Fast & Furious 7' for a period of time so we can assess all options available to move forward with the franchise," Universal Pictures said in a statement.

Four days after the crash that killed the actor and his financial manager, big questions remain unanswered, including:

Did anything go wrong with the vehicle?

The Porsche Carrera GT the two men were in has three times the horsepower of the average car. It's powered by a V-10, 610-horsepower engine. At $450,000 new, it flies down the road and is notoriously difficult to handle.

A top driver has called the car "scary," Autoweek magazine reported.

Rodas was the sixth owner of this one, the magazine said.

Authorities say speed was a factor in the crash. Still, Walker and Rodas were experienced drivers, leading many to question whether something went wrong with the vehicle.

Jim Torp, a car enthusiast who was at the charity event where Rodas and Walker had been just before the crash, said he thought he heard some kind of blast before the car slammed into a light pole. "What the first explosion was -- I don't know if their tire blew up, because it sounded like a tire blew on the car," Torp told CNN on Monday.

How fast were they going?

The area where the crash took place -- a wide business park road in Valencia, California -- has a reputation for being popular with drivers who like the thrill of going fast. In recent years, authorities have tried to stop the speeding in the area.

A 45-mph speed limit sign was on the light pole knocked down by the Porsche. A security camera video, which does not show the car itself, suggests that black smoke started to rise from the vehicle about a minute after the light pole and tree fell.

A Los Angeles County Sheriff's Department investigation is focused on how fast the 2005 vehicle was going.

Skid marks on the asphalt near the crash site, which indicate a car had done doughnut spins, also are being examined, but Torp told CNN that he looked closely at the skid marks and believes they were left by a car with smaller tires.

Was anyone else in danger?

Amid the outpouring of grief for the deaths of Walker and Rodas, many people are also asking whether the ride had endangered pedestrians or other drivers. It took place at 3:30 p.m. Saturday.

Online stories about the crash are filled with comments from readers saying it's fortunate that no one else was killed or injured.

In 2001, when the first "Fast & Furious" movie was released, Walker talked about the dangers of drag racing. "Nothing would be worse than a 120-mile-an-hour blowout, on a surface street, you know, with pedestrians lining up and down. You know, it's just common sense, it's just not worth the risk factor," he said.

Authorities have ruled out drag racing in this accident, and those who knew Walker and Rodas say they were not the sort of people who would risk their lives and others' in a race.