ORLANDO, Fla. — Hien Tran lay dying in intensive care this month after a car accident, as detectives searched for clues about the apparent stab wounds in her neck.

An unlikely breakthrough arrived in the mail a week after she died from her injuries. It was a letter from Honda urging her to get her red Accord fixed, because of faulty airbags that could explode.

“The airbag,” said Tina Tran, the victim’s twin sister. “They said it was the airbag.”

Ms. Tran became at least the third death associated with the mushrooming recalls of vehicles containing defective airbags made by Takata, a Japanese auto supplier. More than 14 million vehicles from 11 automakers that contain the airbags have been recalled worldwide.

When Ms. Tran crashed her car, the airbag, instead of protecting her, appeared to have exploded and sent shrapnel flying into her neck, the Orange County sheriff’s office said. On Monday, in an unusual warning, federal safety regulators urged the owners of more than five million vehicles to “act immediately” to get the airbags fixed.