The blaze broke out on the San Mateo-Hayward Bridge on May 4 because of a catastrophic failure of the rear suspension system, CHP Capt. Mike Maskarich said. The air suspension failure allowed the spinning driveshaft to contact the floor pan, causing friction that ignited carpets and set the vehicle on fire, authorities said.
No charges will be filed, prosecutors said.
"Some tragedies are crimes and some are not, and this one is not," San Mateo County District Attorney Steve Wagstaffe said at a joint news conference with the CHP.
The Public Utilities Commission is fining the limo operator $1,500 for having more passengers than allowed.
The fire broke out while a nurse, Neriza Fojas, was celebrating her recent wedding with a group of friends.
She was among the five killed. Four other friends inside the limo and the limo driver survived.
Recordings of 911 calls released Monday include a woman's voice shouting, "Oh, my god! Oh, my god!" and a man's voice shouting "Get out! Get out!" There also were cries and screams from callers and passengers.
"It's a limousine that's fully engulfed, and there are people trapped inside," one caller said.
A woman who said she was a passenger screamed as she told the dispatcher there were people inside the burning limo.
On another call a rescuer told a dispatcher: "I don't think there is anything we can do."
"The rear of the limo is fully engulfed, and the doors are locked," the rescuer said.
Investigators said one of the rear doors had the child lock engaged, and the other side of the limo was too burned for them to tell.
One caller broke into tears as he described the scene to an operator who reassured him that help was coming.
In interviews with investigators, the survivors described a harrowing escape.
"I had to push Jasmin (Deguia) through the window, and Nelia (Arellano) pulled me out through the driver's side door," Amalia Loyola told investigators during an interview at the hospital hours after the fire, according to the investigation report.
Deguia said she was the third one out.
"When I was getting out of the limousine, the partition was so small my hips got stuck between the partition and the small ledge. I was hanging out headfirst," she said.
Loyola was the last one out.
"We all waited for other people to get out, but no one did," said Deguia.
Authorities reviewed video and photos of the fire and interviewed survivors, including the limo driver, Orville Brown.
Brown, 46, of San Jose, said at first, with the music in the limo turned up, he misunderstood what one of the passengers in the back of the 1999 Lincoln Town Car was saying when she knocked on the partition window.
"I thought she was asking if she could smoke," Brown said in an interview transcript released Monday.
He said seconds later, the women knocked again, this time screaming, "Smoke, smoke!" and "Pull over."
Brown said he got out and "tried to call 911, but it was busy."
Another passenger, Grace Guardiano, said the driver was "standing out there on his phone," after stopping the limo.
"He did not open the doors," Guardiano said. "I went out through the partition and called 911 from outside."
Brown said he helped the four survivors escape through the partition. One of the women ran around to a rear passenger door but by then the vehicle was engulfed in flames.
The state Public Utilities Commission had authorized the vehicle to carry eight or fewer passengers, but it had nine on the night of the fire.
Aerial video shot after the incident showed about a third of the back half of the limousine scorched by the fire. Its taillights and bumper were gone and it appeared to be resting on its rims, but the remainder of the vehicle didn't appear to be damaged.
The investigation found that the suspension and axle travel stops for the differential failed, allowing the spinning driveshaft to rub directly underneath the floor panel. "The heat and possibly sparks, generated from the friction ... ignited the materials covering the floorboard," the report said.
Those materials were the carpet in the backseat.
The report doesn't pinpoint why the air suspension failed, but it said those failures "occur with some frequency, due to the normal wear and aging of the various components."
The probe found no indication that an electrical failure or gas from the fuel system caused or contributed to the fire.
While the chain of events that led to the accident may be unusual, some vehicle safety advocates were troubled that a fire not fed by gasoline could engulf the vehicle.
"Not many vehicles would have that type of failure, nonetheless the overriding question is why does a limousine have so many flammable materials in it? That's what concerns me as a safety advocate," said Clarence Ditlow, executive director of the Center for Auto Safety, a consumer advocacy group.
Fatal accidents involving limousines are rare. From 2002 through 2011, 31 limousine passengers or drivers died in 21 crashes, according to data kept by the National Highway Traffic Safety Administration. Only three of those deaths were related to a fire, all in 2003.
Associates Press writer Justin Pritchard in Los Angeles contributed to this report.