Police officers say Dorner has now become their worst nightmare -- a heavily armed man with the same training they have, plus a military background.
As the search continues, law enforcement officials are wondering whether Dorner has been engaged in diversionary tactics -- leaving a trail of false bread crumbs.
"He's extremely dangerous," said San Bernardino Sheriff John McMahon at a news conference on Friday. McMahon said that his officers, along with law enforcement and the FBI had been searching for Dorner all night, even with SWAT teams in snow-cats on California's Bear Mountain.
Police are trying to figure out if Dorner deliberately dropped his wallet and his LAPD badge in San Diego, where earlier in the week he allegedly attempted to steal a boat to flee to Mexico.
"He knows what he's doing," L.A. Police Chief Charlie Beck told reporters yesterday "We trained him. He was also a member of the armed forces. It is extremely worrisome and scary, especially for the police officers involved."
In a "manifesto" attributed to Dorner posted on the Internet, the former cop boasts about his combat skills, writing that he will utilize every bit of small arms training, demolition, ordnance and survival training he had been given in the LAPD, and in his career in the Navy.
"I know your TTPs (techniques, tactics, and procedures). Any threat assessments you generate will be useless. This is simple," Dorner wrote in his lengthy manifesto. "I will mitigate all risks, threats and hazards. I assure you that Incident Command Posts will be target rich environments."
Dorner is believed to be heavily armed, possessing an assault rifle and other weapons. Dorner also claims to have a .50 caliber rifle, which fires bullets five inches long -- capable of piercing bullet-proof vests, cutting through cars and some armored vehicles. Sources say it is likely that Dorner has such a rifle. The combination is concerning since Dorner's LAPD trainers rated him an "expert" sharpshooter with a .9 millimeter handgun, and "marksman" with an M-16 rifle.
Former FBI agent and ABC News consultant Brad Garrett says Dorner's weapons training and his familiarity with police protocol make him a lethal adversary.
"He knows how to move around and is very familiar with how to use firearms," Garrett said. "And knowing how the LAPD and other departments search for suspects, he will certainly avoid the logical places where police would look, like prior homes or locations that he used. He would also get rid of any electronics that might be used to track him," Garrett said. "He's probably using a prepaid cellphone."
As a former Navy man, Dorner would still have his uniforms, and Garrett says he would not be surprised if he dressed in uniform to help avoid being spotted and identified.
"A uniform has been part of his identity all of his life," Garrett said.
Dorner has already cut a wide path of destruction. Chief Charlie Beck said at a news conference Thursday that Dorner "ambushed" two Riverside, Calif. officers as they sat in their squad car at a traffic light in the early morning hours. One officer, a 35-year-old, 11-year veteran of the force, was killed. His 27-year-old partner was seriously wounded. Garrett said the ambush shows Dorner's skill as a hunter.
"These officers apparently were taken by complete surprise. They didn't know they were being shot at until they were shot."
Dorner is also wanted in the killings of Monica Quan and her fiance, Keith Lawrence, who were found shot to death in their car Sunday night, according to Irvine, Calif. police chief David L. Maggard. Quan is the daughter of a retired LAPD official, and Dorner allegedly threatened him and his family, among others, in his manifesto, according to police.
"Other people besides law enforcement officers have been taken out," Garrett said. "It's clear that he thinks everyone is fair game. This is a dangerous and treacherous guy who, for everyone's safety, he has got to be taken off the street."
Now the manhunt for Dorner is in overdrive, and one source tells ABC News that just about anyone with a badge in southern California is looking for him. Local law enforcement agencies have activated "Code Alex," which triggers local police agencies to take up pre-planned observation posts as part of a mutual aid plan.
U.S. Marshals have obtained a federal warrant for Dorner's arrest and Thursday the FBI executed a search warrant in Las Vegas at a property Dorner is believed to have owned in the past.
Brad Garrett sees a violent end to it all. When asked what he thought the chances were of Dorner surrendering to police, he said, "Below zero. Nothing about his personality indicates he would ever turn himself in. He will either be caught by surprise and taken, or caught in a shootout and go out in a blaze of glory."
Some officials hope that there will be a breakthrough in the next 24 to 48 hours given the surge in media coverage. His face is everywhere; his friends and associates are being run down. His resources are thought to be dwindling. He lost his car, he lost his wallet, and he can't use credit cards. As one law enforcement official put it, "His world is getting smaller every minute."