Attorneys for the two former officers again questioned what killed Thomas. A pathologist testified it was years of meth use.
Dr. Steven Karch told jurors Thomas had an enlarged heart caused by years of methamphetamine use. Karch said Thomas' heart was so weak he could have died anytime at home.
Thomas was taken off life support July 10, 2011, five days after a violent encounter with Fullerton police. Karch says Thomas likely suffered heart failure.
Former Officer Manual Ramos is charged with second-degree murder and former Corporal Jay Cicinelli is facing involuntary manslaughter and excessive force after the death of the 37-year-old homeless man.
Karch, an expert in how drugs affect the heart, testified for the defense for $750 an hour. He disputed the Orange County coroner's finding that Thomas died of lack of oxygen to the brain caused by chest compression and facial injuries.
Thomas' run-in with police was captured on surveillance video. Karch testified Thomas' death was precipitated by a "spontaneous psychotic episode" brought on by his meth use.
An autopsy found no drugs in Thomas. But Karch testified long-term meth use could still cause violent outbursts years after someone stopped using drugs.
Under cross examination, Karch said his only evidence that Thomas suffered a psychotic episode was based on his own opinion that someone would have to be mentally imbalanced to take on six police officers.
Prosecutors will begin to present rebuttal evidence on Thursday.