Three police officers in Oakland, Calif., were gunned down on Saturday and a fourth was critically wounded in an afternoon of violence that began with a routine traffic stop and ended with a grim 9 p.m. news conference to announce the toll of one of the worst days in the police department’s history.

The police said a 27-year-old gunman shot two motorcycle officers after being pulled over at 1:15 p.m. Saturday, killing one and wounding the other. The gunman then fled to a nearby apartment.

A manhunt ensued through the streets of the East Oakland section of the city. When the police tracked down the gunman and burst into the apartment, he shot two more officers with an assault rifle, killing them both, before he was shot dead by the police.