Paul Walker's death was not caused by a mechanical problem with his friend's Porsche Carrera GT and was purely down to excessive speed. There had been some speculation that the super car has a history of difficult handling, but investigators say the driver of the car lost control due to "speed, and speed alone."

Speaking anonymously, investigators also ruled out the chance that debris in the road caused the car to smash into a street light and tree.

The three black boxes recovered from the wreck will determine the exact speed the car was travelling at, as well as determining whether airbags were deployed or not, according to Sky News.

Walker - the star of the Fast and Furious movies - was finally laid to rest at a private ceremony at Forest Lawn Memorial Park Cemetery in Hollywood Hills on Sunday. 

"A few people got up and gave tributes to Paul," a source told US Weekly. "It was hard for many people to talk, they were in tears and couldn't finish what they were saying."

"It was a really sad day for so many people, and you could tell they just weren't ready to say goodbye. His parents were there, along with his brothers and some other family members. Everyone was hugging each other tight and didn't want to let go."

The ceremony followed a public memorial last weekend, when thousands gathered to lay gifts in Santa Clarita, where Paul and friend Roger Rodas died. Fans revved their engines in honour at the event, which was also attended by his co-star Rick Yune.

Paul Walker recently topped Google's Zeitgeist list of the most searched for people of 2013.