Larry James Salter, 55, was being treated for a prescription drug addiction and was going through a detoxification period.
Medical professionals were transporting him to Brookwood Hospital in Birmingham via Interstate 65 when the incident occurred. He was not being transferred to a mental hospital.
The victim jumped from the rear of the moving vehicle in the Gardendale area, a suburb of Birmingham. He died from injuries suffered in the jump.
"All I know is he was being transferred to Brookwood [Hospital] to help him with a sickness that he had..." said Greenville Mayor Dexter McLendon. "He was my friend and he had a sickness."
Salter was laid to rest Monday evening.