LOS ANGELES — A former Navy reservist who was fired from the Los Angeles Police Department in 2008 has gone on a murderous rampage aimed at police officers and their families, law enforcement officials said Thursday, killing at least three people — including an 11-year veteran of the Riverside Police Department — and setting off a huge manhunt across Southern California.

The police were on high alert in a dragnet that appeared to rattle even a part of the country familiar with sweeping police hunts. Protection teams were dispatched overnight to guard uniformed officers and their families, scores of officers set up lines of defense outside the fortress that is the Los Angeles Police Department headquarters, and motorcycle officers were ordered to retreat to the safety of patrol cars.

In Torrance, two women delivering newspapers were shot and wounded by police officers who mistook the Toyota pickup they were driving for the one identified as belonging to the gunman, a gray Nissan. About 12 hours later in San Diego, squads of police cars, in a blaze of red lights and screeching tires, converged on a motel where the suspect was mistakenly thought to be hiding after his wallet was found on a sidewalk.