A special needs student was found dead in the back of an empty California school bus and his family believes he was left there all day he died, according to reports.

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The family of 19-year-old Hun Joon Lee, who was autistic and unable to speak, believes the boy stayed on the bus for nine hours.

The boy, also known as Paul, was supposed be to dropped off at school at 8:30 a.m. and would return home around 3:30 p.m, his family told NBC Los Angeles.

When Paul did not return home on Friday, his mother called the school who then contacted the bus company. A driver went to the bus yard where they found the young man inside. He was found unconscious and slumped to the side, according to reports.

The Whittier School District, where Lee was a student, would not say if the teen was in class on Friday.

The family also claims that it was a different bus driver that picked Paul up that morning.

The family set up a GoFundMe account to help pay for expenses.

“My family is completely torn apart and heartbroken, knowing what he had felt during those painful hours," the late teen’s sister, Ellen, wrote on the account's page.

"Inside the bus was about 120-130 degrees and Paul was trapped in there for almost nine hours without a single drop of water. We are hit so hard with this sudden tragedy," she wrote.

The GoFundMe account has already gained more than $18,000 in donations.

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No arrests have been made in the death but police are treating the death as suspicious.

Whitter Police Officer Brad White said: “Nothing that we've learned so far would lead us to believe he had any medical conditions,” according to Fox News.

Whittier Union High School District Superintendent Valerie Thorstenson said: "This tragedy has devastated all of us. We are still gathering information about what happened. The district is calling for a speedy and thorough investigation to determine how something like this could happen."

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She added: "Our hearts are with our student's parents and family -- we're all grieving. We're making ourselves, our counseling services and our staff available to his family and to our students.”

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