Orange County Dist. Atty. Tony Rackauckas said prosecutors would not pursue charges against a third Fullerton officer accused in the Thomas case. That officer's trial was pending.
"I don't intend to proceed with another trial when the two officers here were acquitted," he told reporters.
The jury took less than a full day of deliberation to reach the not-guilty verdicts.
Rackauckas told jurors the former officers had abused their authority on the July evening when they confronted Thomas.
Ramos was facing second-degree murder and involuntary manslaughter charges, and Cicinelli was charged with involuntary manslaughter and excessive use of force under the color of authority.
The incident, captured on surveillance tape, was shown repeatedly during the trial, but each side drew different conclusions as to what it showed.