The parents of a teenage girl who died of heat stroke in the family car at Madera South High School last year have sued BMW and the Madera Unified School District.

The lawsuit, filed Tuesday in Madera County Superior Court, claims the automaker and school district were negligent. It also accuses BMW of North America LLC of product liability and breach of warranties.

Graciela Martinez, 14, became trapped inside a 1997 BMW 328i because of the vehicle’s “double-locking mechanism,” the lawsuit says. Once the doors are locked from the outside, they can’t be opened from the inside.

Graciela also couldn’t use the car’s horn to get help because it needs the ignition key to activate it, the lawsuit says.

“It’s a sad, terrible tragedy that could have been prevented,” said Fresno attorney Warren Paboojian, who represents Graciela’s parents, Pedro and Jacinta Martinez. The family is seeking unspecified damages from the automaker and Madera Unified.

Madera Unified is negligent, Paboojian said, because school officials failed to discover Graciela in the locked car and violated school policy by failing to notify her parents that their daughter was not in class.

Madera Unified Superintendent Ed Gonzalez said Thursday that “the loss is incomprehensible. Our hearts go out to the Martinez family.” Because it is pending litigation, Gonzalez said he could not comment on the accusations in the lawsuit.

On the morning of Sept. 11, Oscar Martinez drove his sisters, Patricia and Graciela, to school. Oscar went to a zero-period class that began at 6:40 a.m. and Patricia went on campus to socialize, the lawsuit says. Graciela remained in the car to sleep before her class began at 7:40 a.m.

Paboojian said Oscar Martinez locked the car doors so no one would bother his sister while she slept. He didn’t know that locking the doors from the outside would trap his sister inside, he said.

Around 3 p.m., Oscar Martinez returned to the car. He unlocked the doors and found his sister in the back seat. “She was pale in color and did not have a pulse,” the lawsuit says.

She was pronounced dead a short time later. “An autopsy revealed that she had died of heat stroke and environmental hyperthermia due to vehicle entrapment,” the lawsuit says.

Graciela Martinez had no phone to call for help and her family knew nothing about the BMW’s double-locking feature, Paboojian said.

Paboojian said Graciela removed some clothing as the car reached triple-digit temperatures. There also are signs she struggled to break out, but she was too small to break a window, he said.

“She was a good kid and nearly a straight-A student,” Paboojian said.

Paboojian contends in the lawsuit that BMW knew of the dangers of the double-locking device because it warns its customers of it in the owner’s manual. The Martinez family, however, was not the original owner of the car and the manual was long gone, he said.

The lawsuit alleges BMW “ignored and suppressed data regarding deaths and serious injuries due to the double-locking mechanism contained in the BMW 328i.”

If BMW had placed a safety-release lever inside the vehicle or recalled the vehicle and fixed the locking device, Graciela’s death could have been prevented, Paboojian said.