San Bernardino County sheriff's deputies conduct door-to-door search in Big Bear, Calif, Thursday, Feb. 7, 2013. Thousands of police officers hunted Thursday for one of their own: a former Los Angeles officer angry over his firing and sought in a deadly shooting rampage after warning he would wage "warfare" on those who wronged him, authorities said. AP Photo/Jae C. Hong Police tape surrounds a bullet-damaged Los Angeles Police vehicle on Thursday Feb. 7, 2013 in Corona, Calif. Former Los Angeles police officer Christopher Dorner is suspected if shooting at the two LAPD officers in the vehicle, who were sent to Corona to protect someone Dorner threatened in a rambling online manifesto. Thousands of police officers throughout Southern California and Nevada hunted Thursday for Dorner, who was angry over his firing and began a deadly shooting rampage that he warned in an online posting would target those on the force who wronged him. FBI agents gather outside a Las Vegas home owned by former Los Angeles police officer Christopher Dorner while collecting evidence, Thursday, Feb. 7, 2013. San Bernardino County sheriff's deputies search a home during a manhunt for former Los Angeles officer Christopher Dorner in Big Bear, Calif, Thursday, Feb. 7, 2013. The ex-Los Angeles police officer who authorities say went on a killing spree to punish those he blamed for his firing killed three people, set off a manhunt that stretched across three states and into Mexico, and stirred fear throughout the region. LOS ANGELES (AP) - A fired police officer who threatened to bring "warfare" to the Los Angeles Police Department went on a shooting rampage that left a policeman and two others dead and set off an extraordinary manhunt that had three states and Mexico on alert for much of Thursday. The search for Christopher Dorner led hair-trigger officers to mistakenly shoot at innocent citizens and forced police to guard their own. But the focus of police efforts shifted Thursday afternoon to the snowy mountains around Big Bear Lake, about 80 miles east of Los Angeles, where police found Dorner's 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. "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 snow storm 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. 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. Thursday was the anniversary of his first day on the job at the department eight years ago. Dorner said in his online rant that after his dismissal that he lost everything, including his relationships with his mother, sister and close friends. 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. Tami Abdollah can be reached on Twitter at www.twitter.com/LATams