Ravitch said at a news conference that Erick Gelhaus, who has been with the sheriff's office for 24 years, acted in self-defense when he shot Andy Lopez. The boy was shot seven times in a vacant lot near Santa Rosa in October.
"The law provides for a complete defense of anyone who defends himself or others," Ravitch said.
Gelhaus and his partner said they ordered Andy to drop the pellet gun he was holding. Instead, they said, he turned towards them, still holding the gun, which did not have the orange tip required by federal law for toy and replica guns.
The FBI is investigating the shooting for possible civil rights violations, and Andy's family has filed a lawsuit in U.S. District Court.
The shooting sparked large demonstrations last year. Protesters gathered outside Ravitch's office during her news conference.