Thomas, 37, died five days after a violent confrontation with six officers in July 2011. The incident was caught on surveillance video.
Former Fullerton police officer Manuel Ramos was charged with second-degree murder and involuntary manslaughter, and former police corporal Jay Cicinelli was charged with involuntary manslaughter and excessive force. Both men pleaded not guilty to the charges.
The trial came to a close after Orange County District Attorney Tony Rackauckas wrapped up his rebuttal to the defense's closing arguments. He told jurors that Ramos had a "duty of care for Kelly Thomas."
"A duty not to put Kelly Thomas at risk of harm by third parties, and that was a continuing duty. And that duty didn't stop when the force began," Rackauckas said.
Rackauckas argued that surveillance video shows proof that Ramos abused his authority, turning a routine encounter into a deadly one with his threat. But defense attorneys say the video shows officers followed their training and police department policy when dealing with an uncooperative, combative suspect.
On Wednesday, defense attorneys wrapped up their arguments saying the prosecution did not prove their case that the officers caused Thomas' death. They argued that Thomas died because of an enlarged heart caused by years of methamphetamine use.
"We don't have a controversy here about the cause of death," Rackauckas said, and then went through with jurors the testimony of doctors who each said Thomas died from a lack of oxygen caused by chest compression and facial injuries.
Ramos is the first law enforcement officer in Orange County to be charged with a homicide for an on-duty death. The jury concluded its first day of deliberations without reaching a verdict. Deliberations will resume at 9 a.m. Monday.