Recent reports point in the direction that a mechanical failure was the reason for, or at least a contributing factor to, the crash. According to the workshop where the car was stored and maintained, it suffered from a leakage in the steering system.
This story quickly grows even worse:
Paul Walker's 15-year old daughter and Roger Rodas' 8-year old son both witnessed the crash.
They were reportedly still alive when the car caught fire/exploded, debate now seems more focused on whether they were unconscious or not.
Both bodies burnt beyond recognition, dental records needed in order to confirm identities.
And the list goes on.
My condolences to his family, friends and fans.
As many has pointed out on various boards across the Internet, he may not have been the best actor out there - even though certainly far worse exists - but he seems to have been very good-natured and genuine person. His enthusiasm for cars notwithstanding, he was a voluntary helper at natural disasters and animal rescues, he was involved with and even spearheaded many charity projects, he was a full-time father, he was never part of any sort of scandals (DUIs, drugs, brawls, etc) that more or less seem to be the norm rather than the exception in Hollywood these days.
The world is full of people doing good in order to become famous, but not equally so of people using their fame to do good.
I salute Paul Walker's memory for his contributions to the world, that even they're rather insignificant when taking the whole picture into account is still more than most of us manage. May he rest in peace.