Los Angeles county sheriff commander Mike Parker said in a statement: "Investigators determined the cause of the fatal solo-vehicle collision was unsafe speed for the roadway conditions."
Parker said although the red 2005 Porsche Carrera GT – driven by Walker's friend and business partner Roger Rodas at the time of the crash – had been modified to boost outputs of its 450kW/590Nm 5.7-litre V10 engine, the investigation concluded there were no pre-existing issues with the car that would have caused the fatal November 30 collision.
Occurring in a 45mph (72km/h) zone in Santa Clarita, California, the crash was preceded by the car traveling at speeds of up to 93mph (150km/h) prior to Rodas losing control and crashing into trees and a power pole.
According to investigators, there were no eyewitnesses to the crash with the sheriff’s department and California Highway Patrol relying on security camera footage from the area for evidence, as well as information and assistance provided by both Porsche and Michelin.
The Los Angeles county coroner's office determined in January that traumatic injuries and burns claimed Walker’s life, while Rodas died as a result of multiple injuries.
The investigation further found that both driver and passenger were wearing seatbelts at the time of the crash and neither had any drugs or alcohol in their system.
The star of the Fast and Furious franchise was 40, Rodas 38.
Filming for Fast and Furious 7 was already underway at the time of the crash, and Universal Pictures has delayed the film's release by nine months to April 10, 2015. Recent reports suggest a mix of body doubles and CGI will be used to complete Walker's unfinished scenes.