The 'Fast and the Furious' star and pal, Roger Rodas, were involved in a fatal accident after the 2005 Porsche Carrera GT they were travelling in crashed into a lamppost in Santa Clarita, California, on November 30, and investigators believe that "speed alone" caused them to veer off the road.
A law enforcement official, who asked to remain anonymous, said they found no evidence that the car had mechanical problems or that debris or other road conditions caused the car to go out of control.
The source said: "We're looking at speed and speed alone."
The car appeared to have spun out of control after Roger, who was driving, negotiated a curve in an industrial park, and the official added: "They were well out of the curve when they lost control."
Officials have already calculated the speed range at which they believe the car was travelling but the figure won't be released until Porsche engineers from Germany fly out to Los Angeles next month to analyse the brakes, engine and body of the wreckage, which will help them determine the exact speed at the time of impact.
The 40-year-old actor's death certificate ruled he died from "combined effects of thermal and traumatic injuries".
Paul's body was cremated last Thursday (12.12.13) and he was laid to rest at the Forest Lawn Memorial Park in Los Angeles' Hollywood Hills on Saturday (14.12.13).