An autopsy on Walker's remains, which had to be identified through dental records, was conducted Tuesday and the results were released Wednesday.
TMZ said Walker, 40, did not die from the impact of the crash alone, he also suffered fatal burns when the Porsche GT he was riding in as a passenger crashed into a tree and a pole, and then burst into flames.
The driver, Walker's longtime friend, Roger Rodas, was also killed.
Rodas, 38, died from multiple traumatic injuries sustained upon impact, TMZ said. Burning was not listed as a factor in his death.
Both deaths were ruled accidents, the celebrity news website said.
Toxicology test results for both men are expected to be released in six to eight weeks.
The cause of the crash remains under investigation, but police have said speed was a factor.