Authorities say a 19-year-old man has been found dead on a Southern California school bus.

Whittier police say the vehicle was parked in a school bus yard at about 4:30 p.m. Friday when the man was found. Officers arrived to find several bus drivers trying to perform CPR on the man, but he was declared dead at the scene.

The Los Angeles Times reported that the man was a special needs student at the Sierra Education Center.

There were no signs of trauma on the young man's body and no weapons found at the scene, Brad White, a spokesman for the Whittier Police Department, told the Times.

The young man typically leaves school on the bus around 2:30 p.m. and arrives home at 4 p.m., White said. When he didn't show up on Friday, his mother called the school and the school called the bus company. A driver went out to the bus yard and found the young man in the parked bus, White said.

Whittier Union High School District Supt. Sandra Thorstenson issued a statement of condolence.

Officials say the cause of death has yet to be determined, and it wasn't clear why he was on the bus when it was parked in the school district yard.