A California Highway Patrol officer was killed and two others injured in a shootout on Monday evening in Riverside, Calif., that also left a suspect dead and commuters scrambling for safety during the evening rush, the authorities said.

One officer was in critical condition at a hospital late Monday night and another received minor injuries, according to Scott Parker, assistant chief of the Highway Patrol’s inland division. Two civilians were also wounded, he said at a news conference.

The confrontation began when a driver was pulled over for a traffic stop at about 5:30 p.m. near Interstate 215 in Riverside, about 60 miles east of downtown Los Angeles. It was not clear why he was stopped.

A Highway Patrol officer was planning to impound the man’s white pickup truck and called for a tow truck, Chief Parker said at the news conference. But as the officer was filling out paperwork, the man pulled out a rifle and shot the officer.

He called for backup, and several other police officers arrived at the scene. The gunman shot two more Highway Patrol officers, Chief Parker said, and a fourth Highway Patrol officer who arrived at the scene fatally shot the gunman.

“It was a long and horrific gun battle,” Chief Sergio G. Diaz of the Riverside Police Department said at the news conference.

The first Highway Patrol officer who was shot was flown to a nearby hospital and died, Chief Parker said. Gov. Gavin Newsom identified the officer as A. M., 34.

On Tuesday, the coroner’s office in Riverside County identified the gunman as Aaron Luther, 49, of Beaumont, Calif., and The Associated Press reported he had an extensive criminal record that included a conviction for attempted murder in the 1990s.

Chief Diaz said the authorities did not believe there were additional suspects, adding that investigators would try over the next few days to piece together what the gunman’s motive might have been.

“We don’t know where the suspect was coming from, where he was headed to, what his affiliations are,” Chief Diaz said. “We don’t know his motive for this crime.”