Updated

A California prosecutor said he hasn't seen evidence suggesting police tried to kill a homeless schizophrenic man who died after a violent confrontation with officers in the college town of Fullerton.

"As far as intentional killing — whether an officer intended to kill him ... I have not seen any evidence of that in this case," Orange County District Attorney Tony Rackauckas told the Los Angeles Times.

His office is trying to determine whether the six Fullerton officers used excessive force when they confronted 37-year-old Kelly Thomas on July 5. The officers were investigating reports of a break-in at a Fullerton transit hub and tried to search Thomas' backpack when they got into a fight with him.

Thomas suffered severe head and neck injuries and was taken off life support five days later.

Rackauckas said his office is trying to expedite the criminal investigation by adding extra investigators.

He told the Orange County Register he has not ruled out any charges. Speaking in general, he said prosecutors can file murder charges if they find that officers acted with such malice that it approached an intent to kill. He said prosecutors could also file involuntary manslaughter charges if they find that the officers used excessive force.

The coroner's office has not determined a cause of death because it is waiting for results of toxicology tests.

Thomas' father told the Times that MRI and X-ray results from the hospital that treated his son showed he suffered a severe brain injury caused by a lack of oxygen and blunt force trauma.

Ron Thomas, who earlier released a graphic photo of his son's bloody, swollen and barely recognizable face, said the facial bones had also been broken.

Kelly Thomas' death has sparked outrage in the suburb southeast of Los Angeles. A bystander recorded the incident with a cell phone. A bus surveillance tape showed agitated witnesses describing how officers beat Thomas and used a stun gun on him repeatedly as he cried out for his father.

Rackauckas said he has seen a surveillance tape from the bus depot that prosecutors and police have refused to make public. He declined to describe its content, saying only that it "shows a lot and there is a lot it doesn't show."

The police department has called the case an isolated incident and put the officers on administrative leave.

The FBI is also investigating.