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 served a search warrant on his mother's house in the Orange County city of La Palma. Dorner's mother and sister were there at the time, and a police spokesman said they were cooperating.
The manhunt had Southern California residents on edge. Unconfirmed sightings were reported near Barstow, about 60 miles north of the mountain search, at Point Loma base near San Diego and in downtown Los Angeles.
Some law enforcement officials speculated that he appeared to be everywhere and nowhere, and 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 deep canyons, 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 the trail of tracks that had led them away from his truck but offering the possibility of new trails 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 has the advantage of strength in numbers and access to resources, such as special weapons, to bring him in.
"We're prepared to use our expertise in terms of special weapons and tactics to address any threat that he poses," LAPD Deputy Chief Kirk Albanese said. "We're working with other agencies ... to make sure we take the advantage of our side as much as we can."
In his online rant, Dorner sprinkled in military and police parlance, seemingly baiting authorities.
"Any threat assessments you generate will be useless," it read. "This is simple. I know your TTP's (techniques, tactics, and procedures) and PPR's (pre-planned response). I will mitigate any of your attempts at preservation."
Without the numbers that authorities have, Dorner will likely rely on the element of surprise, experts said.
"He doesn't even have to stand and fight," Hall said. "He makes his shot of opportunity and flees."
It's an advantage that Dorner is well aware of. In his posting, he wrote: "I have the strength and benefits of being unpredictable, unconventional, and unforgiving. Do not waste your time with briefs and tabletops.
"Whatever pre-planned responses you have established for a scenario like me, shelve it," he said.
Authorities said they do not know how long Dorner has 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.
"If he is not prepared to wait that out, or he hasn't done it before, not everybody is survivor-man," Sparks said.
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 typically given out as a souvenir by the LAPD police chief was also in the package, riddled with bullet holes.
Police believe that indicates some level of pre planning.
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 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, Albanese said.
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 buzzing about the manhunt but went about their usual routine. Jackie Holohan, who runs a vacation rental company, said visitors weren't dissuaded from coming to the mountain resort despite the intensive manhunt.
"The only ones who have called want to make sure if they can get up the mountain," Holohan said.
Law enforcement officials, meanwhile, said they will continue to search for Dorner through the weekend in Big Bear. They were also inspecting his truck for clues and were following up on multiple theories, including whether he intentionally left it there.
"Here's the bottom line, we don't know," Albanese said.
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