LOS ANGELES — A fired police officer who threatened to bring "warfare" to the Los Angeles Police Department allegedly went on a shooting rampage that left a policeman and two others dead and set off an extraordinary manhunt Thursday that put Southern California on edge, led hair-trigger officers to mistakenly shoot at innocent citizens and forced police to guard their own.

The search for Christopher Dorner had three states and Mexico on alert before shifting Thursday afternoon to the snowy mountains around Big Bear Lake, about 80 miles east of Los Angeles, where police found his burned-out pickup truck and tracks leading away from the vehicle.

San Bernardino County Sheriff John McMahon said 125 officers were going door to door and attempting to track the suspect, and that a SWAT team was providing added security to those in the community. Schools were put on lockdown while investigators examined the vehicle and spread out across the area.

"He could be anywhere at this point, and that's why we're searching door to door," McMahon said, adding that the manhunt would continue "as long as we can." A snowstorm was expected in the region with temperatures dipping into the teens overnight.

Said LAPD Assistant Chief Michel Moore: "This complex and violent investigation has led to this mountain."

The pickup was to be processed at a crime lab Thursday evening and examined by investigators from multiple agencies.

Throughout the day, thousands of heavily armed officers patrolled highways throughout Southern California, while some stood guard outside the homes of people police say Dorner vowed to attack in a rant posted online. Electronic billboards, which usually alert motorists about the commute, urged them to call 911 if they saw him.

"I will bring unconventional and asymmetrical warfare" to Los Angeles Police Department officers, on or off duty, said the manifesto. It also asserted: "Unfortunately, I will not be alive to see my name cleared. That's what this is about, my name. A man is nothing without his name."

Dorner, 33, had several weapons including an assault rifle, said police Chief Charlie Beck, who urged him to surrender at a news conference held amid heightened security in an underground room at police headquarters.

"Of course he knows what he's doing; we trained him. He was also a member of the armed forces," he said. "It is extremely worrisome and scary."

The nearly 10,000-member LAPD dispatched officers to protect more than 40 potential targets, including police officers and their families. The department also pulled officers from motorcycle duty, fearing they would make for easy targets.

"I never had the opportunity to have a family of my own, I'm terminating yours," the manifesto said.

At one point, officers guarding one location mistakenly opened fire on a pickup truck, believing it matched the description of Dorner's dark-colored 2005 Nissan Titan. Two occupants were injured.

The search for Dorner, who was fired from the LAPD in 2008 for making false statements, began after he was linked to a weekend killing in which one of the victims was the daughter of a former police captain who had represented him during his disciplinary hearing. Thursday was the anniversary of his first day on the job at the department eight years ago.

Earlier Thursday, two LAPD officers en route to provide security to one of Dorner's possible targets, were flagged down by a resident at a gas station in Corona who reporting seeing the suspect. The officers then followed a pickup truck until it stopped. The driver, believed to be Dorner, got out and fired a rifle, police said. A bullet grazed an officer's head.

Later, two officers on routine patrol in neighboring Riverside were ambushed at a stoplight by a motorist who drove up next to them and opened fire with a rifle. One died, and the other was seriously wounded but was expected to survive, Riverside police Chief Sergio Diaz said.

Diaz said news organizations should withhold the officers' names because the suspect had made clear that he considers police and their families "fair game."

The hunt for Dorner also led to two errant shootings in the pre-dawn darkness Thursday.

LAPD officers guarding a target named in the manifesto shot and wounded two women in suburban Torrance who were in a pickup truck, authorities said. Beck said one woman was in stable condition with two gunshot wounds and the other was being released after treatment.

"Tragically we believe this was a case of mistaken identity by the officers," Beck said.

Minutes later, Torrance officers responding to a report of gunshots encountered a dark pickup matching the description of Dorner's, police said. A collision occurred and the officers fired on the pickup. The unidentified driver was not hit and it turned out not to be the suspect vehicle, they said.

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In San Diego, where police say Dorner tied up an elderly man and unsuccessfully tried to steal his boat Wednesday night, Naval Base Point Loma was locked down Thursday after a Navy worker reported seeing someone who resembled Dorner.

Navy Cmdr. Brad Fagan said officials believe Dorner had checked into a base hotel on Tuesday and left the next day without checking out. Numerous agencies guarded the base on Thursday. Fagan said Dorner was honorably discharged and that his last day in the Navy was last Friday.

Nevada authorities also joined the search, because Dorner owns a house nine miles from the Las Vegas Strip, according to authorities and property records.

Associated Press writers contributing to this report include Jeff Wilson, Bob Jablon, Greg Risling, Shaya Tayefe Mohajer, Linda Deutsch and John Antczak in Los Angeles and Ken Ritter in Las Vegas.