MARTINEZ  (AP) — The suspect killed in a shootout following a traffic stop on a San Francisco Bay Area freeway had shot a California Highway Patrol officer in the head without warning, leaving him in critical condition, authorities said Wednesday.

Footage from a dashboard camera showed Officer Kenyon Youngstrom speaking with Christopher Boone Lacy, who had been pulled over Tuesday morning, Contra Costa County Sheriff's spokesman Jimmy Lee said. Without provocation, Lacy pulled his gun and shot Youngstrom, Lee said.

Moments later, Youngstrom's partner shot Lacy in the head, Lee said. Lacy, 36, of Corning, Calif., was later pronounced dead at a hospital.

Youngstrom's partner, whose name has not been released, apparently initiated the stop from a separate patrol car on Interstate 680 near Alamo, flagging Lacy for suspicion of driving with an obstructed license plate, Lee said at a news conference.

Youngstrom, 37, was already on the shoulder handling a dead deer when his partner notified him that he was pulling the Jeep over. Youngstrom then directed the suspect to pull over and approached the Jeep, Lee said.

Youngstrom and Lacy spoke for about "30 to 40 seconds" before Lacy shot the officer, Lee said. Investigators later found in Lacy's vehicle a loaded semi-automatic handgun, two ammunition magazines and a knife, Lee added.

A motive for the shooting remains unknown as investigators are still trying to develop a profile of Lacy, Lee said.

"We've been told he pretty much keeps to himself. He's a loner," Lee said.

Lacy had a prior drunken driving arrest in Marin County in 2006, Lee said. Beyond that, Lacy had no criminal record.

A team of investigators late Tuesday served a search warrant at Lacy's home and seized six computers and several hard drives, Lee said.

Investigators also talked to Lacy's parents, who live in Oregon are expected to come to the area for questioning, Lee added.

Youngstrom is a married father of four children and a seven-year veteran of the force. Dozens of his fellow officers and law enforcement colleagues held a vigil at John Muir Medical Center in Walnut Creek on Tuesday with his family members, some of whom came up from Southern California.

A neighbor, Ryan Patchen, told the San Francisco Chronicle (http://bit.ly/TWu8Gx ) Youngstrom was devoted to his family and job.

"You know it's a risk, but you don't expect it to happen, especially something so close to home," Patchen, 22, said. "I feel awful for his family, what they must be going through."