Law enforcement officers working in falling snow searched a California mountain for a sacked police officer who threatened to bring "warfare" to the Los Angeles Police Department and went on a shooting rampage that left a policeman and two others dead.
More than 100 officers were searching for Christopher Dorner in the San Bernardino Mountains east of the city after finding his burnt-out truck and footprints.
"We're going to continue searching until either we discover that he left the mountain or we find him, one of the two," San Bernardino County Sheriff John McMahon said at a news conference.
A search of dozens of homes in the Big Bear community failed to find Dorner, and the search was concentrating deeper in the mountains, near the place where his burnt-out truck was found, the sheriff said.
Officers followed what appeared to be Dorner's tracks from the truck but lost them on the frozen ground, Mr McMahon said. "There's a lot of cabins up there that are abandoned. We want to make sure that he didn't find a place to hide out for the night," he said.
In Los Angeles, the head of the police department's detective bureau said all options in the search were being kept open. "Here's the bottom line: We don't know if he's on foot or not," said Deputy Chief Kirk Albanese. "Is he on foot up on the mountain? Is he down the mountain? We don't know."
The search for Dorner, 33, stretches across California, Nevada, Arizona and northern Mexico. LAPD officers are especially on edge because Dorner, who was fired from the force in 2008 after three years, promised in rambling writings to bring "warfare" to police and their families.
Thousands of heavily armed officers patrolled highways throughout Southern California, while some stood guard outside the homes of more than 40 people police say Dorner vowed to attack in a rant posted online.
"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 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.