The cause of Ye Meng Yuan's death was "multiple blunt injuries that are consistent with being run over by a motor vehicle," Robert J. Foucrault said at a press conference in San Mateo, Calif.
"She was alive at the time," he said.
Ye Meng Yuan was one of three people, of a total 307 passengers and crew aboard the plane, who died as a result of the July 6 crash. Her classmate, 16-year-old Wang Linjia, died in the crash itself while 15-year-old Liu Yipeng died in hospital July 12 as a result of injuries sustained in the crash.
The San Francisco Police and the National Transportation Safety Board are both investigating what caused the crash and how the rescue of passengers and crew from the burning Boeing 777 unfolded.
San Francisco Fire Department Chief Joanne Hayes-White said Friday that the fire department is examining every aspect of its response to the crash.
"The coroner's finding [is] very difficult and devastating news for all of us," she said.
Hayes-White said Ye Meng Yuan was likely run over by one of the aircraft rescue firefighting vehicles that is part of the fire crew based at the airport but said it is unclear whether one or more vehicles were involved in the accident.
She said it was not yet clear what role fire-retardant foam played in obscuring the girl. It was reported earlier that foam that had been applied to suppress the fire on the aircraft may have covered up the girl and prevented the driver of the fire truck from seeing her.
The fire chief said her department has reached out to the girl's family and offered to meet with them face to face but has so far not spoken with any members of the family.
"There's not a lot of words for how badly we feel about it, how sorry we feel about it," she said.