SAN FRANCISCO (AP) — Officers shot and killed a man Thursday after he led them on a lengthy high-speed chase, crashed in downtown San Francisco and then fired a gun at good Samaritans who tried to help him, authorities said. The chase through three counties and over two bridges ended with the wreck at a busy intersection in the financial district, where morning traffic was snarled while police investigated. The incident began in the Contra Costa County city of Richmond shortly before 5 a.m., when the man allegedly carjacked a woman driving a white Cadillac Escalade.