Carmen Verdugo said she installed a hidden camera in her home when she noticed bruises on her daughter's body and changes in her behavior after receiving in home behavioral therapy from Kevin Yeun, who at the time was working for California Pediatric and Family Services.
Marcela has autism, a brain birth defect, and can't speak.
"It was frightening for the parents not to be able to ask her, "Hey, is anything bad happening to you?'" said attorney Robert Glassman.
On behalf of the Verdugo family, Glassman filed a complaint in court Tuesday against Yeun and the Azusa-based company he once worked for.
Glassman provided an edited and excerpted video which shows Yeun hitting Marcela several times.
"We are looking to reform the policies and procedures that were in place at this company that somehow allowed a man like this to slip through the cracks," Glassman said.
California Pediatric and Family Services has not replied to a request for comment.
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Yeun was arrested, convicted and sentenced to probation and one year of child abuse treatment classes.