This comes after the attorney representing the family of the man, Kelly Thomas, released medical records on Wednesday.
They showed that Thomas suffered broken bones in his face and cracked ribs. The records also showed that he choked on his own blood and was repeatedly shocked with two stun guns.
Thomas, who suffered from schizophrenia, was declared brain dead five days after the altercation. The violent clash came as officers were investigating reports of someone burglarizing cars at a transit hub in Fullerton.
Garo Mardirossian, the attorney for Thomas' family, said one of the six officers involved in the beating caused the most egregious injuries with a stun gun.
"[The officer] held it sort of like a pistol and pistol whipped him repeatedly by pounding him on his head. As that officer did that, he caused serious injury and eventual brain death," said Mardirossian.
The Orange County coroner has not released an autopsy report.
"We didn't analyze these. Professional doctors did, so we're listening to them and their interpretations. They tell me clearly that Kelly was murdered," said Thomas' father, Ron.
Thomas' death has sparked outrage in Fullerton with calls for the police chief to resign. So far, none of the six officers involved in the incident have been arrested and no charges have been filed against them. They were placed on paid leave.