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.