REDWOOD CITY, Calif. -- The livery company that operated the limo that burst into flames, claiming the lives of five women en route to a Bay Area bridal party, will be fined $7,500 but won't face criminal charges, law enforcement officials said Monday.

A three-month investigation into the May crash deemed it "accidental in nature." 

The car was carrying two more passengers than was legal, officials said during a news conference, adding that the state would fine the company  for failing to operate it safely. But the extra passengers were not determined to have played any part in the blaze.

"This is a horrific tragedy," said San Mateo County Dist. Atty. Stephen Wagstaffe. "It changed lives forever. But it is not a case that goes to the criminal courts. … This is a tragedy that is not a crime."

Foster City Fire Chief Michael Keefe said that the stretch limousine's suspension system had failed as it traveled west on the San Mateo-Hayward Bridge about 10 o'clock on a Saturday night. The vehicle was carrying a 31-year-old nurse who had recently married, along with eight of her friends.

The 1999 Lincoln Town Car's rotating drive shaft came in contact with the floorboard, Keefe said, causing friction, heat and possibly sparks and igniting the materials covering the floorboard.

"As the fire developed, it ignited the foam padding and other material used to fabricate the rear seat," Keefe said.

The flames and resulting smoke "blocked access to the rear doors of the limo, leaving the passengers with one possible exit — through the small pass-through opening into the driver's compartment," he said. "Tragically, not all passengers were able to exit in time."

Photos included in the report released Monday showed a white limo with a black top. The front of the vehicle appeared intact. The rear was severely damaged: the passenger-side back door burned through, the rear tires flattened and wheels melted, the trunk blistered and peeling.

CHP Capt. Mike Maskarich said that the investigation included a thorough inspection of the car and analysis of its maintenance records and the business records of LimoStop Inc., the company that owned and operated it. Officials also conducted extensive interviews with the witnesses and survivors.

"We have concluded that the fire was accidental in nature," Maskarich said.

Although some though the driver may have been on his cellphone, Maskarich said phone records showed he was not.

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maria.laganga@latimes.com