Autopsies are scheduled Tuesday for "Fast and Furious" actor Paul Walker and his friend who were killed in a fiery car crash over the weekend in Santa Clarita, coroner officials said.

The Los Angeles County coroner has yet to officially identify the actor and his friend, Roger Rodas, as the two victims in part because their bodies were badly burned, requiring the use of dental records.

Authorities, meanwhile, have not determined what caused the crash about 3:30 p.m. Saturday on Hercules Street, but are investigating if speed played a factor. Rodas was driving the 2005 red Porsche Carrera GT when it slammed into a tree and concrete pole, bursting into flames.

PHOTOS: Paul Walker, 1973-2013

The high-performance Porsche was not street racing at the time, the men’s friend Jim Torp told reporters at the crash site Monday. And L.A. County sheriff's officials say eyewitnesses did not see a second car.

The Porsche had already been sold, so the men were not going out to be reckless, Torp added.

“I’m a good friend of theirs and I’m fighting for them because there’s been a lot of speculation about them drag racing, and that did not happen,” he told reporters.

He recalled how the tragedy unfolded, starting from the moment when Walker and Rodas slowly pulled out of the driveway as a charity event was winding down. A California Highway Patrol officer was parked just down the street, he added.

After they came back around for another pass and went out of sight, he and another car enthusiast listened to the sounds of the Porsche's exhaust to gauge its speed.

"You could hear the exhaust -- they got on it a little bit -- and I heard two booms," Torp said.

Smoke was visible from Always Evolving Performance Motors, a shop owned by Rodas that is located around the corner from the crash site.

Actor Vin Diesel, who co-starred in the "Fast and Furious" series with Walker, visited the crash site Monday night, addressing a crowd of mourners using a loudspeaker from a Los Angeles County Sheriff's Department car.

"If my brother were here today. And if he saw all the love you were bringing here. If he could see for himself that [you have] shown my brother love ... it's going to stay with me forever ... showing that angel up in heaven how much you appreciated him," he said.

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joseph.serna@latimes.com

Twitter: @josephserna