Why didn't the driver simply throw the transmission into neutral as officers urged him to do? Why didn't a safety mechanism activate that was supposed to cut power to the engine in such situations? And could he have made the story up in pursuit of fame and money?
Each question is getting scrutiny from the Internet-consuming public as they question the motives of the driver, a 61-year-old real estate agent named James Sikes. Some skeptics have even invoked the infamous in expressing doubts about the story.
No evidence has emerged to suggest that Sikes was dishonest when he called 911 on Monday to report that the accelerator of his 2008 Prius was jammed during a trip home from his lawyer's office.
Listen to an excerpt of the 911 call
Sikes and his car emerged unscathed, but the incident has been another major headache for the Japanese automaker amid questions over the safety and reliability of its vehicles.
The California Highway Patrol has repeatedly said it has no reason to suspect a hoax. It does not plan to investigate the incident or perform a mechanical inspection because there were no injuries or property damage. Investigators from Toyota and the federal government are also looking into the incident.
"There is no factual information that I'm aware of, or the highway patrol is aware of, that would discredit his story," agency spokesman Brian Pennings said Friday.
Sikes twice this week about his ordeal, but he has not sought out attention or talk show interviews like others have done during their 15 minutes of fame. Pennings said he urged Sikes to speak with reporters the first time, on Monday, after the white-knuckled journey down Interstate 8 to avoid getting besieged later by the media.
And a law firm representing Sikes during the investigation said its client does not intend to take legal action against the automaker.
Doubters have asked why Sikes didn't put the car in neutral as a California Highway Patrol dispatcher and an officer repeatedly urged him to do. Sikes said he considered going into neutral but worried he might go into reverse or flip.
"I had never played with this kind of transmission, especially when you're driving, and I was actually afraid to do that," he said Tuesday. "I was afraid to do anything out of the normal."
Toyota has said all Priuses are equipped with a computer system that cuts power to the wheels if the brake and gas pedals are depressed at the same time, as Sikes was doing.
"It's tough for us to say if we're skeptical. I'm mystified in how it could happen with the brake override system," Don Esmond, senior vice president of automotive operations for Toyota Motor Sales, said Thursday.
Raj Rajkumar, an electrical and computer-engineering professor at Carnegie Mellon University in Pittsburgh who studies auto electronics, said the Prius could still have acceleration malfunctions even with the fail-safe system.
Toyota says the fail-safe and the engine are controlled by a central computer that contains two independent microprocessors that communicate and must agree with each other. If there's a disagreement, power would be cut to the wheels.
But Rajkumar said the two engine control unit microprocessors could still receive common erroneous signals from sensors or experience software errors that could cause the throttle and the fail-safe mechanism to malfunction.
Sikes came to a stop after a Highway Patrol officer , telling him to push the brake pedal to the floor while applying the emergency brake. Sikes apparently did this, allowing him to slow the car to 50 mph and shut off the engine.
At one point during the 911 call, the dispatcher asks if he can press the ignition button for five seconds and she gets no response. Sikes said later that he struggled to hold the phone and keep his hands on the wheel.
More on Toyota's Troubles:
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Todd Neibert, the officer who gave instructions to Sikes over a loudspeaker, said he smelled burning brakes when he caught up with the Prius. He examined the car when it came to a stop.
"The brakes were definitely down to hardly any material," he told reporters. "There was a bunch of brake material on the ground and inside the wheels."
Sikes said afterward that he was "embarrassed" by the incident, suggesting that he wished he would have handled it differently. "I'm just embarrassed about that," he said. "You have to be there. That's all I can say."
Kurt Bardella, a spokesman for Rep. Darrell Issa, R-Calif., said Friday that investigators are best positioned to determine if there was a hoax, but no evidence has emerged.
A representative of Issa's office was at a California Toyota dealership when investigators from the National Highway Traffic Safety Administration and Toyota examined Sikes' blue Prius on Wednesday and Thursday.
"Where are these suggestions coming from?" he said. "It would be irresponsible to assert it's a hoax without having facts."
Joan Claybrook, a former NHTSA administrator, said Sikes' refusal to shift to neutral, is understandable.
"It's such a horrifying experience to be completely out of control," she said. "It's the kind of thing you dream about when you're really upset and you wake up in sweats."
The same firm handling Sikes' case also represents the family of California Highway Patrol Officer Mark Saylor, which sued Toyota last week in San Diego Superior Court.
Saylor was killed in August along with his wife, her brother and the couple's daughter after their Lexus accelerator on a freeway in La Mesa, near San Diego. Their loaner car hit a sport utility vehicle and burst into flames.
Representatives of the firm did not respond to phone messages seeking additional comment Friday.
Claybrook, the former federal administrator, noted that drivers often come under heavy scrutiny for reporting unintended acceleration.
"Attacking the driver has long been the answer that not just Toyota, but the entire industry, has had," she said. "Blaming the driver is old hat."