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 have been hampered by a heavy winter storm in the area. Dorner, a former Los Angeles police officer, is accused of carrying out a killing spree because he felt he was unfairly fired from his job. AP Photo/Pool, The Inland Valley Daily Bulletin, Will Lester 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 job, Friday, Feb. 8, 2013, in Big Bear Lake, Calif. AP Photo/Chris Carlson (AP) - All that was left were footprints leading away from Christopher Dorner's burned-out pickup truck, and enormous, snow-covered mountains where he could be hiding among hundreds of cabins, deep canyons and dense woods. More than 100 officers, including SWAT teams, were driven Friday in glass-enclosed snow machines and armored personnel carriers to hunt for the former Los Angeles police officer suspected of going on a deadly rampage to get back at those he blamed for ending his police career. With bloodhounds in tow, officers went door to door as snow fell, 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. The bad guy is out there, he has a certain time on you, and a distance. How do you close that?" asked T. Gregory Hall, a retired tactical supervisor for a special emergency response team for the Pennsylvania State Police. "The bottom line is, when he decides that he is going to make a stand, the operators are in great jeopardy," Hall said. 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. 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, ordinance and survival training I've been given" to bring "warfare" to the LAPD and its families. At noon, police and U.S. marshals accompanied by computer forensics specialists used a search warrant to remove about 10 paper grocery bags of evidence from his mother's single-story house in the Orange County city of La Palma. Dorner's mother and sister cooperated with the search, and a police spokesman said. 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. Bad weather grounded helicopters with heat-sensing technology. After the discovery of his truck Thursday afternoon, SWAT teams in camouflage started scouring the mountains. As officers worked through the night, a storm blew in, possibly covering tracks that had led them away from his truck but offering the possibility of a fresh trail to follow. "The snow is great for tracking folks as well as looking at each individual cabin to see if there's any signs of forced entry," said San Bernardino County Sheriff John McMahon. 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. "He can be behind every tree," Hall said. He can try to draw them into an ambush area where he backtracks. Authorities said they do not know how long Dorner had been planning the rampage. It's not clear if he is familiar with the area, or has 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. In Big Bear Lake on Friday, residents were on edge about the manhunt even as ski slopes remained open. "A lot of people are frightened by it," said Dennis Pitner. A lot of people are at home locked in their houses and probably won't come out for a couple more days, maybe even longer. 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.