The woman's husband thought Torres tried to rob his wife, so he contacted sheriff's deputies walking nearby and pointed the suspect out, sheriff's officials said according to CBSLosAngeles.
Authorities said Torres was uncooperative and that he initially refusing to take his hands out of his pockets.
They also said he was fighting with deputies as they tried to restrain him.
But while the suspect was on the pavement, one deputy is seen elbowing him and stomping on his head.
The incident was captured because by chance a film crew from Telemundo were across the street.
The cameraman ran over when he saw the commotion and then captured the assault on camera.
Torres had minor facial injuries after the incident.
Sheriff's spokesman Steve Whitmore told the LA Times a 24-year-old deputy has been relieved of his duty, but did not name him.
It is unusual for deputy uses of force to be criminally investigated.
'We take this very seriously, and we are going to get to the bottom of exactly what happened,' Mr Whitmore told the newspaper.
Torres was booked for sexual battery, battery on a peace officer and possessing counterfeit identification and is being held in lieu of $20,000 bail.
He is currently in a housing unit for people with possible mental illness in the Los Angeles County Jail.
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