Orange County District Attorney Tony Rackauckas told jurors that former officer Manuel Ramos and former corporal Jay Cicinelli acted with unreasonable force and violated police procedure during the confrontation with Thomas.
Rackauckas showed footage from dramatic surveillance video that captured the violent struggle.
"As you watch, you realize that what you're watching and hearing is a person dying at the hands of the police," Rackauckas said. "You're watching a homicide."
Ramos is charged with second-degree murder and Cicinelli is charged with involuntary manslaughter.
On Monday, two doctors -- one for the defense, one for the prosecution -- had very different versions of what killed 37-year-old Thomas. Prosecutors say Thomas died due to lack of oxygen, but the defense argues Thomas could have died at any time because of a weak heart damaged by prior methamphetamine use.
"He didn't die just because he had a weak and diseased heart. I think you can clearly see that," Rackauckas said. "He died from a prolonged struggle with several police officers."
However, the defense maintains that the officers were doing their job, handling a man who started using meth in the 10th grade, and who suffered from violent unpredictable outbursts.
"This case isn't about a bully cop who was trying to just beat down a homeless guy. It's about a police officer who for 10 years protected his community," said John Barnett, Ramos' attorney.
Jurors were told that Thomas attacked his grandfather with a fireplace poker in 1995.
"Whether he was doing this because he took drugs when he was a kid, whether he was doing it because he was mean, he still presented a danger," said Barnett.
The defense pointed out how the cause of death is still at question and stressed to the jury that prosecutors need to prove what the cause of death was. But Rackauckas denied that, saying, "What matters is that the police killed him."
The defense will continue with its closing arguments Wednesday. The case could go to the jury as early as Wednesday afternoon.