The manhunt had Southern California residents on edge. Some law enforcement officials speculated that he appeared to be everywhere and nowhere, and that he was trying to spread out their resources.
The focus was on the mountains east of Los Angeles — a snowy wilderness, filled with deep canyons, thick forests and jagged peaks. Bad weather grounded helicopters with heat-sensing technology.
Property records show his mother owns undeveloped land nearby, but a search of the area found no sign of him.
In his online rant, Dorner seemed to taunt authorities.
"I have the strength and benefits of being unpredictable, unconventional, and unforgiving," he wrote.
Authorities said they did not know how long Dorner had been planning the rampage. 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.
Jamie Usera, an attorney who befriended Dorner when they were college students, said he introduced him to the outdoors and taught Dorner about hunting and other outdoor activities.