The massive dragnet for a fugitive ex-cop continued Friday, with more than 100 officers conducting a fruitless search in the snowy, forested mountains around Big Bear Lake for an armed gunman who police say is on a vengeful rampage. 
 
 As the falling snow piled up, authorities pledged to continue the manhunt until they find Christopher Jordan Dorner, the 33-year-old former Los Angeles police officer suspected of killing three people, or stumble on definitive evidence that he is no longer in the area. 
 
 The trail has gone cold since Dorner's Nissan Titan pickup was found Thursday morning engulfed in flames on a U.S. Forest Service dirt road between the Bear Mountain and Snow Summit ski resorts. A set of footprints in the snow led away from the burned truck. It took more than five hours for experts to confirm that it was Dorner's vehicle and search parties to begin a methodical sweep of an area stretching across eight square miles. 
 
 While ski-masked SWAT teams went door-to-door checking hundreds of homes and shuttered cabins, other authorities fanned out on foot, slogging through fresh snow with search dogs. The teams combed backcountry and checked every shed, trash bin and barrel where the fugitive could hide. Dorner is described as African American, 6 feet tall and 270 pounds. 
 
 The snow slowed the search, but did not halt it, said Cindy Bachman, a spokeswoman for the San Bernardino County Sheriff's Department. Sheriff John McMahon said the snow has one advantage: It is "great for tracking folks." 
 
 Although following tracks led only to frustration Friday, authorities were relieved by the break in a week of extraordinary interconnected violence. 
 
 Police say that Dorner has killed three people and injured others in a campaign to take revenge on those he blamed for his dismissal from the LAPD four years ago. Investigators are scrutinizing a conspiracy-laden manifesto that they believe was published on Dorner's Facebook page. In the screed, Dorner threatened "unconventional and asymmetrical warfare" against police officers and their families, saying that he has no choice but to kill to reclaim his damaged reputation. 
 
 Police accuse him of killing the daughter of a retired LAPD captain and her fiance, who were found shot to death Sunday in a car in Irvine. While on the run, police said, Dorner shot three police officers, one fatally, in Riverside County. 
 
 With warnings on radio and TV that an armed and deadly fugitive remained at large, police spent hours chasing down bogus leads and erroneous sightings. 
 
 Dorner was purportedly driving a white Lexus near Barstow. He was supposedly spotted entering the county jail in downtown Los Angeles. He was allegedly holed up in a hotel in San Diego or in a park in Norco or at a home next to the Barona Indian Reservation in San Diego County. None of those tips checked out, and authorities are considering false reporting charges against one person who was more prankster than tipster. 
 
 "When you're dealing with a case that's getting this amount of press coverage, you're going to get your share of bad information," said Laura Eimiller, a spokeswoman for the FBI, whose agents searched Dorner's home in Las Vegas and are investigating a package that CNN received, apparently from Dorner, that made various threats. Federal and local authorities also searched the home of his mother, Nancy Dorner, in La Palma, carrying out bags of potential evidence. 
 
 With the possibility of Dorner in the vicinity and the potential for violence, the Bear Valley Unified School District closed all its campuses Friday, and nervous residents locked their doors and made other preparations. 
 
 Roger Curtis, a retired carpenter who lives in Big Bear, said he was watching the manhunt on TV when a car alarm sounded. "I got the guns and loaded them," he said. 
 
 Many residents suspect that Dorner high-tailed it out of the area, but others believe he could be hunkered down in one of many vacant, half-hidden cabins. 
 
 Authorities can only speculate about Dorner's familiarity with the terrain and preparedness to brave a winter storm. Nancy Dorner owns property about 35 miles away in Arrowbear Lake, according to county records. Dorner, who was trained as a police officer and a Navy Reserve officer, learned to hunt in the Utah wilderness as a college student. 
 
 As much as 8 inches of snow fell at higher elevations Friday. The National Weather Service predicts that temperatures will plunge to 16 degrees early Saturday, with the wind chill making it equivalent to -6. 
 
 If Dorner were still hiding in the woods, he would need layered, insulated clothing — and have to avoid getting wet — to survive for very long, said Dr. Brian Prestwich, an assistant professor of clinical family medicine at USC's Keck School of Medicine. Cold weather poses a tremendous, and often unappreciated, threat to human survival. 
 
 "The minute you're exposed to the cold air or you get wet, the clock starts ticking," Prestwich said. 
 
 Dorner's five-hour-plus head start before the search got underway has brought extensive speculation about his whereabouts, including theories from his former boss, retired LAPD Police Chief William J. Bratton. 
 
 Bratton and John Miller, a former LAPD official who is now a CBS correspondent, said they thought the burned truck was "possibly a diversionary tactic to draw people into that area while he's actually heading south." 
 
 The former chief has good reason to be concerned about Dorner's location: In the package Dorner purportedly sent to CNN was a ceremonial coin with Bratton's name on it and three bullet holes — a discovery Bratton called "chilling." 
 
 Police continue to guard at least 40 people mentioned in the anger-filled manifesto. 
 
 Miller speculated that the burning of Dorner's pickup showed potential for calculated "pre-staging" and "planning." If this is premeditated staging, he said, "It makes you wonder: What is his plan for the end game?" 
 
 phil.willon@latimes.com 
 
 joseph.serna@latimes.com 
 
 ken.weiss@latimes.com 
 
 Times staff writers Andrew Blankstein, Ari Bloomekatz, Eryn Brown, John Glionna, Anna Gorman, Robert Lopez, Kate Mather, Rick Rojas and Richard Winton contributed to this report. ||||| The hunt for Christopher Dorner in the snow-covered San Bernardino Mountains is expected to resume at daybreak Saturday, when authorities hope clearer skies will allow airplanes to help them in their search. 
 
 Members on the California Highway Patrol search a truck for Christopher Dorner, a former Los Angeles police officer accused of carrying out a killing spree because he felt he was unfairly fired from his... (Associated Press) 
 
 This undated photo released by the Los Angeles Police Department shows suspect Christopher Dorner, a former Los Angeles officer. Dorner, who was fired from the LAPD in 2008 for making false statements,... (Associated Press) 
 
 Police investigators take away evidence from the home of the mother of fugitive suspect former Los Angeles police officer Christopher Dorner, in La Palma, Calif., on Friday, Feb. 8, 2013. Police agencies... (Associated Press) 
 
 A digital billboard along Santa Monica Boulevard on the west side of Los Angeles shows a "wanted" alert for former Los Angeles police officer Christopher Dorner Friday, Feb. 8, 2013. Dorner is suspected... (Associated Press) 
 
 A San Bernardino County Sheriff SWAT team returns to the command post at Bear Mountain near Big Bear Lake, Calif. after searching for Christopher Jordan Dorner on Friday, Feb. 8, 2013. Search conditions... (Associated Press) 
 
 A San Bernardino County Sheriff SWAT team returns to the command post at Bear Mountain near Big Bear Lake, Calif. after searching for Christopher Jordan Dorner on Friday, Feb. 8, 2013. Search conditions... (Associated Press) 
 
 A San Bernardino County Sheriff SWAT team returns to the command post at Bear Mountain near Big Bear Lake, Calif. after searching for Christopher Jordan Dorner on Friday, Feb. 8, 2013. Search conditions... (Associated Press) 
 
 ADDS DATE VIDEO WAS TAKEN - This image provided by the Irvine Police Department shows Christopher Dorner from Jan. 28, 2013 surveillance video at an Orange County, Calif., hotel. More than 100 officers,... (Associated Press) 
 
 Relentless snowfall on Friday grounded helicopters with heat-sensing technology and hampered their effort to find the former Los Angeles police officer suspected of going on a deadly rampage to get back at those he blamed for ending his career. 
 
 After they found his burned-out pickup truck near at this ski resort town Thursday afternoon, SWAT teams in camouflage started scouring the mountains, aware to the reality they could be walking into a trap set by the well-trained former Navy reservist who knows their tactics and strategies as well as they do. 
 
 "He can be behind every tree," said T. Gregory Hall, a retired tactical supervisor for a special emergency response team for the Pennsylvania State Police. "He can try to draw them into an ambush area where he backtracks." 
 
 As authorities weathered heavy snow and freezing temperatures in the mountains, thousands of heavily armed police remained on the lookout throughout California, Nevada, Arizona and northern Mexico for a suspect bent on revenge and willing to die. 
 
 Police said officers still were guarding more than 40 people mentioned as targets in a rant they said Dorner posted on Facebook. He vowed to use "every bit of small arms training, demolition, ordnance and survival training I've been given" to bring "warfare" to the LAPD and its families. 
 
 The manhunt had Southern California residents on edge. Unconfirmed sightings were reported near Barstow, about 60 miles north of the mountain search, and in downtown Los Angeles. 
 
 Some law enforcement officials said he appeared to be everywhere and nowhere, and speculated that he was trying to spread out their resources. 
 
 For the time being, their focus was on the mountains 80 miles east of Los Angeles _ a snowy wilderness, filled with thick forests and jagged peaks, that creates peril as much for Dorner as the officers hunting him. 
 
 The small army hunting him has the advantage of strength in numbers and access to resources, such as special weapons, to bring him in. 
 
 In his online rant, Dorner baited authorities. 
 
 "Any threat assessments you generate will be useless," it read. "I have the strength and benefits of being unpredictable, unconventional, and unforgiving." 
 
 Without the numbers that authorities have, Dorner holds one advantage: the element of surprise. 
 
 Authorities said they do not know how long Dorner had been planning the rampage or why he drove to the San Bernardino Mountains. Property records show his mother owns undeveloped land nearby, but a search of the area found no sign of him. 
 
 It was not clear if he had provisions, clothing or weapons stockpiled in the area. Even with training, days of cold and snow can be punishing. 
 
 "Unless he is an expert in living in the California mountains in this time of year, he is going to be hurting," said former Navy SEAL Clint Sparks, who now works in tactical training and security. "Cold is a huge stress factor. ... Not everybody is survivor-man." 
 
 Jamie Usera, an attorney in Salem, Ore., who befriended Dorner when they were students and football teammates at Southern Utah University, said he introduced him to the outdoors. Originally from Alaska, Usera said, he taught Dorner about hunting and other outdoor activities. 
 
 "Of all the people I hung out with in college, he is the last guy I would have expected to be in this kind of situation," Usera, who had lost touch with Dorner is recent years, told the Los Angeles Times. 
 
 Others saw Dorner differently. Court documents obtained by The Associated Press on Friday show an ex-girlfriend of Dorner's called him "severely emotionally and mentally disturbed" after the two split in 2006. 
 
 Dorner served in the Navy, earning a rifle marksman ribbon and pistol expert medal. He was assigned to a naval undersea warfare unit and various aviation training units, according to military records. He took leave from the LAPD for a six-month deployment to Bahrain in 2006 and 2007. 
 
 Last Friday was his last day with the Navy and also the day CNN's Anderson Cooper received a package that contained a note on it that read, in part, "I never lied." A coin riddled with bullet holes that former Chief William Bratton gave out as a souvenir was also in the package. 
 
 Police said it was a sign of planning by Dorner before the killing began. 
 
 On Sunday, police say Dorner shot and killed a couple in a parking garage at their condominium in Irvine. The woman was the daughter of a retired police captain who had represented Dorner in the disciplinary proceedings that led to his firing. 
 
 Dorner wrote in his manifesto that he believed the retired captain had represented the interests of the department over his. 
 
 Hours after authorities identified Dorner as a suspect in the double murder, police believe Dorner shot and grazed an LAPD officer in Corona and then used a rifle to ambush two Riverside police officers early Thursday, killing one and seriously wounding the other. 
 
 The incident led police to believe he was armed with multiple weapons, including an assault-type rifle. That detail concerned officers whose bullet-proof vests can be penetrated by such high-powered weapons, said LAPD Deputy Chief Kirk Albanese. 
 
 As a result, all LAPD officers have been required to work in pairs to ensure "a greater likelihood of coming out on top if there is an ambush," Albanese said. "We have no officers alone right now." 
 
 ___ 
 
 Associated Press writers contributing to this report include Michael Blood and John Antczak in Los Angeles and Julie Watson in San Diego. 
 
 Risling reported from Big Bear Lake and Abdollah reported from Los Angeles. She can be reached on Twitter at http://www.twitter.com/LATams
– Authorities may have found Christopher Dorner's burned-out truck near Big Bear Lake in California, but the former cop and suspected murderer remains at large this morning, reports the Los Angeles Times. A storm has brought heavy snow and bitter-cold temperatures to the area, which is both a help and a hindrance to the manhunt. Dorner would need serious survival gear if he is indeed still in the woods somewhere. His mother owns undeveloped land in the region, but a search of it turned up nothing. Of course, given Dorner's boasts of planning to bring "warfare" to the LAPD, authorities have to be on guard that they're not walking into a trap, reports AP. Or that he didn't plant the truck there to divert resources while he heads elsewhere. "It makes you wonder," says a former LAPD official. "What is his plan for the end game?"