The county jail in downtown Los Angeles was in lockdown Friday as a precaution after a civilian female employee of the Twin Towers Correctional Facility spotted someone fitting Dorner's description, said Los Angelese County sheriff's spokesman Steve Whitmore.
U.S. Navy installations throughout California and Nevada were "maintaining a heightened security posture," a U.S. military official told CNN.
"Security personnel are on the lookout" for Dorner, the official said. The measure was ordered overnight by Rear Adm. Dixon Smith, commander of the Navy's southwest region.
The official declined to discuss security procedures, but said the move was made after it became clear that Dorner earlier this week gained access to the Naval Base at Point Loma and stayed in a motel there.
Two sailors reported that he approached them Wednesday and spoke with them for about 10 minutes. The conversation took place at a coastal "riverine" unit in San Diego where Dorner served in 2006. As a Navy reservist, Dorner held security jobs with that unit.
The Navy is not certain whether Dorner still possesses any military identification he might try to use to enter a facility. The official said an investigation is under way to determine what military identification he might have.
Dorner underwent flight training in 2009 at Naval Air Station Fallon in Nevada before serving in San Diego.
In La Palma, California, about 22 miles southeast of Los Angeles, police searched Friday the home of Dorner's mother, where she and a daughter were cooperating with investigators, said Lt. Bill Whalen of the Irvine Police Department.
The 270-pound former Navy lieutenant promised to bring "unconventional and asymmetrical warfare" to police officers and their families, calling it the "last resort" to clear his name and retaliate at a department that he says mistreated him.
Dorner is wanted in the killings on Sunday of two people in Irvine and in the shooting of three Los Angeles-area police officers Thursday, one of whom died.
One of the victims of the Irvine killings, Monica Quan, was the daughter of the retired police officer who represented Dorner in his efforts to get his job back, police said.
"My opinion of the suspect is unprintable," Riverside police Chief Sergio Diaz said, hours after one of his officers was killed. "The manifesto, I think, speaks for itself (as) evidence of a depraved and abandoned mind and heart."
Here's what is known so far:
-- Dorner, who worked as an LAPD officer from 2005 to 2008, is accused of killing Quan and her fiance Sunday in Irvine, then shooting two Riverside police officers and an LAPD officer Thursday. Police say he unleashed numerous rounds at the Riverside officers, riddling their car with bullets and killing a 34-year-old officer. The second officer in the car was seriously wounded, and the LAPD officer suffered only minor injuries, police said.
-- In a lengthy letter provided by police, Dorner said he had been unfairly fired by the LAPD after reporting another officer for police brutality. He decried what he called a continuing culture of racism and violence within the department, and called attacks on police and their families "a necessary evil that I do not enjoy but must partake and complete for substantial change to occur within the LAPD and reclaim my name."
-- Leads have taken police from Los Angeles to San Diego to Las Vegas to Big Bear Lake, where police found the charred carcass of Dorner's gray pickup. Police had found no trace of him Friday, the San Bernadino County sheriff said. Trackers lost footprints believed to be Dorner's in a wooded area near the truck.
-- The LAPD and other agencies have gone to extremes to protect officers. Forty teams of officers were guarding people named as targets in Dorner's letter. On Thursday, one of the teams shot at a pickup that resembled Dorner's but turned out to be a Los Angeles Times newspaper delivery vehicle.
-- Despite Dorner's statement in the letter that "when the truth comes out, the killing stops," Los Angeles police Chief Charlie Beck said authorities don't plan to apologize to Dorner or attempt to clear his name. Dorner's firing, Beck said Thursday, had already been "thoroughly reviewed."
-- In Nevada on Thursday, FBI agents searched Dorner's Las Vegas home. The search forced some of Dorner's neighbors out of their homes for several hours, CNN affiliate KLAS reported.
"It's too close to home. It's kind of scary," neighbor Dan Gomez told KLAS.