The incident happened April 10 on board a San Bernardino city bus. The video shows a passenger attacking a autistic man.
San Bernardino police said a viewer recognized the suspect as 44-year-old Ronald Jackson.
Jackson is a parolee and was already in custody. Officers said he'd been arrested the day after the assault on a carjacking charge.
The 36-year-old victim suffered minor injuries, but he will recover.