The Porsche carrying Fast & Furious star Paul Walker was travelling approximately 145 km/h when it lost control on a suburban street and crashed, killing the actor and his friend, the Los Angeles County Sheriff said on Tuesday, concluding an almost four-month investigation.

"Investigators determined the cause of the fatal solo-vehicle collision was unsafe speed for the roadway conditions," Los Angeles County Sheriff Commander Mike Parker said in a statement.

The sports car slammed into a light pole which had a speed limit sign of 45 mph (about 72 km/h), killing Walker and Roger Rodas in a fiery wreck.

Parker said the 2005 model-year high-powered sports car had been modified to increase its horsepower.

Investigators calculated that Rodas was driving between 130 km/h and 151 km/h when his 2005 Porsche Carrera GT began to drift as it lost control after coming out of a curve.

No evidence of mechanical problems

The Associated Press reported in December that investigators had found no evidence that the car had mechanical problems and ruled out debris or other roadway conditions.

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A 2011 file photo shows actor Paul Walker at a photo call of the movie Fast and Furious 5, in Rome. (Andrew Medichini/Associated Press)

Subsequently, Porsche sent engineers to California to review the rare car's wreckage. Though it was badly mangled and burned, the engineers were able to do a thorough analysis. They found no problems with the car's electrical systems, brakes, throttle, fuel system, steering, suspension or other systems.

Porsche declined a request for comment Tuesday.

The conclusion about the speed was based on a "yaw" mark on the road that the car's tire left on the road in an area of industrial office parks in Santa Clarita, about 48 kilometres northwest of downtown Los Angeles. Witnesses told a sheriff's deputy that they thought the car could have been travelling in excess of 160 km/h.

Post-crash investigators noted several issues with the condition of the car, which had several prior owners, including IndyCar driver Graham Rahal:

  • Its original exhaust system had been modified in a way that could allow it to go faster, but also could have been done to change its sound.
  • Its tires were about nine years old; the owner's manual suggests changing the tires after four years.
  • Its left rear brake rotor was worn below manufacturer specifications, but that did not contribute to the crash.

Rodas, 38, and Walker, 40, had taken what was supposed to be a quick ride from a fundraiser benefiting Reach Out Worldwide, a Walker charity that gives first-response aid to victims of natural disasters. The crash occurred near the fundraiser, and horrified friends of the men raced to the scene. 

Paul Walker obit

A publicist for actor Paul Walker says the star of the "Fast & Furious" movie series has died in a car crash north of Los Angeles Saturday afternoon. He was 40. No further details were released. (AP Photo/The Santa Clarita Valley Signal, Dan Watson) (Dan Watson/The Santa Clarita Valley Signal/Associated Press)

While Rodas was Walker's financial adviser, the two had bonded over their shared love of fast cars. They co-owned an auto racing team named after Rodas' shop, Always Evolving, and Rodas drove professionally for the team on the Pirelli World Challenge circuit in 2013.

Walker starred in all but one of the six Fast & Furious blockbusters, which glorify muscular cars and risky driving.

With files from Reuters