LOS ANGELES >> A driver stopped by police pulled out a rifle and opened fire, killing a California Highway Patrol officer and wounding two others during a shootout on a freeway overpass that left the gunman dead and sent terrified motorists running for cover.

Officer Andrew Moye, Jr., died in the gunfight as dozens of bullets flew late Monday afternoon in Riverside, east of Los Angeles. Two civilians received minor injuries.

One wounded officer was in critical condition and the other was serious but both are expected to survive, Riverside Police Officer Ryan Railsback said today.

Moye had pulled over a pickup truck and was doing paperwork to impound it when the driver, who was outside the vehicle, reached in, grabbed a rifle and fatally wounded the officer. Moye was able to radio for help and other officers engaged in a “long and horrific gun battle,” Riverside Police Chief Sergio Diaz said.

Authorities said it was unclear what prompted Moye to stop the truck or for the driver to open fire.

Moye’s flag-draped body was removed from a hospital and placed in a hearse Monday night. Motorcycle officers then led a procession as the hearse was driven to the county coroner’s office.

“I am devastated by the tragedy,” CHP Commissioner Warren Stanley said in a tweet. Gov. Gavin Newsom ordered flags at half-staff today at the state Capitol.

Relatives said Moye was 33 and had been with the CHP for about four years.

“He was so kind,” his stepmother, Debbie Howard, told KTVU-TV. “You’re not going to hear one bad word about him. He loved this job.”

Police did not identify the gunman but Dennis Luther told multiple media outlets that the shooter was his son, Aaron Luther, 49, of nearby Beaumont.

Dennis Luther said he watched the events unfold on television. “It’s hard. I love him. And I’m sorry for the policeman,” he told KABC-TV. “I’m devastated. I just can’t believe it.”

After his truck was impounded, Aaron Luther called his wife to pick him up, his father said. When she arrived, the tow truck was there.

“She said she heard ‘pop, pop, pop’ … gunfire, and then a bullet went through the windshield of her car,” Dennis Luther said.

He said his son served prison time for attempted murder but was released more than a decade ago. As a felon, he wasn’t supposed to have a gun and Dennis Luther said he’s not sure how his son came to possess one.

Dennis Luther said his son recently seemed depressed, was having knee pain and marital problems but was devoted to his two children and a stepchild.

“He lived for his kids. That’s what motivated him,” Luther said. “So I don’t know what overcame him. I mean, I wish I did know.”

Jennifer Moctezuma, 31, of Moreno Valley, told the Los Angeles Times she was driving home with her 6-year-old twins when a bullet flew through her front windshield. Charles Childress, 56, a retired Marine from Moreno Valley, was in the car behind her.

He led the family as they crawled to the bottom of a bridge to hide as the bullets flew.

“He’s my hero,” Moctezuma said.

Jim Pasco, executive director of the Fraternal Order of Police, said traffic stops and domestic violence calls are the most dangerous situations for police.

“You have no idea who’s in the car, what they’re up to, whether they’re armed,” Pasco said. “A police officer stopping a car on the side of the road doesn’t know anything about the driver.”

Pasco said it’s not unusual for officers to impound a car at the scene, or to let someone return to his or her vehicle.

“It’s situational,” he said. “He might have been asked for his registration and said ‘it’s in the car.’”