WHITTIER, Calif. -- The family of a special needs student found dead Friday on a school bus says he may have been stuck for hours in sweltering heat, CBS Los Angeles reports.

Hun-Joon Lee, 19, was discovered by a bus driver around 4:20 p.m. in a parking lot. The school district in Whittier, Calif., has not said if the student showed up for class Friday.

Police said Lee's mother notified his school when he didn't return home at 4 p.m., the usual time.

On a GoFundMe page set up to raise money for Lee's family, a writer claiming to be Lee's sister writes that the teen, nicknamed Paul, "was trapped in there for almost nine hours without a single drop of water."

"My family is completely torn apart and heartbroken, knowing what he had felt during those painful hours. Inside the bus was about 120-130 degrees," she wrote.