LOS ANGELES (CBSLA) — A 14-year-old girl is dead and her 12-year-old sister in grave condition Thursday after were struck by a big rig while they walked to school in the Exposition Park area of Los Angeles.

The crash happened about 8 a.m. near 37th Street and Broadway, about a block away from Clinton Middle School, according to the Los Angeles Police Department.

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Both victims were taken to a nearby hospital, where one of them later died.

The driver of the big rig remained on scene and was cooperating with investigators, police said. He was not arrested and was visibly upset.

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A witness, who is a student at the school, told police she saw the whole collision.

“She waved her hands to get attention to the driver to stop, he got out of his car and stopped, and finally realized he had run over these two girls,” said LAPD Detective Moses Castillo.

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Police were looking into reports the trucker may have been distracted by his cell phone. It’s unclear whether the driver will be criminally charged.