Chief: He's 'trained assassin'

NEW: Mountain search for ex-cop Christopher Dorner scaled back "If you turn yourself in, then you will be safe," LAPD chief says Dorner claims LAPD racism cost him his job and declared war on the department Border agents are searching cars crossing into Mexico for signs of Dorner

Big Bear Lake, California (CNN) -- A scaled-back search for a renegade former Los Angeles police officer resumed Sunday morning in the San Bernardino Mountains as the city's police chief called on Christopher Dorner to surrender.

The Los Angeles Police Department says the cashiered cop declared war on his former comrades and their families and has killed three people since last weekend. In an interview aired Sunday on CNN affiliate KCBS, Chief Charlie Beck called Dorner a "trained assassin" but said he wouldn't be harmed if he gave himself up.

"If you turn yourself in, then you will be safe and nobody else has to die," Beck said. "If you don't, if you decide to try to take the life of another Los Angeles police officer or their family member, then you'll have to suffer the consequences."

The dragnet was in action Sunday around the Big Bear Lake resort, about 90 miles east of Los Angeles, where investigators found Dorner's burning pickup Thursday afternoon. After working through a weekend of heavy snow and overnight temperatures in the single digits, police officers, sheriff's deputies and federal agents tried again to pick up Dorner's trail, San Bernardino County sheriff's spokeswoman Lehua Pahia said.

The day's effort began with about 60 officers -- but by early afternoon, it had been scaled back to about 25 investigators, aided by a helicopter equipped with body-heat sensors and other specialized equipment, Pahia said. None of the tips the department had received so far has panned out, she said.

The LAPD fired Dorner, a former Navy officer, in 2009 after finding he had falsely accused his training officer of using excessive force on a mentally ill man. Dorner challenged his firing in court and lost, and in a manifesto released last week, he blamed racism and corruption in the department for his removal.

Beck announced Saturday that the LAPD would re-examine its proceedings against Dorner -- "not to appease a murderer," but "to reassure the public that their police department is transparent and fair in all things we do."

"I am aware of the ghosts of the LAPD's past, and one of my biggest concerns is that they will be resurrected by Dorner's allegations of racism within the department," Beck said.

'Last resort'

In the manifesto posted online, 33-year-old Dorner promised to bring "unconventional and asymmetrical warfare" to officers and their families, calling it the "last resort" to clear his name and strike back at a department he says mistreated him.

According to authorities, Dorner began making good on his threats a week ago when he allegedly killed Monica Quan and her fiance, Keith Lawrence, in a parking lot in Irvine, south of Los Angeles.

Quan was the daughter of a now-retired Los Angeles police officer who represented Dorner in a disciplinary hearing that led to his termination.

Time line in hunt for Dorner

Significance of suspect's torched truck Weather hampers search for former cop Accused killer's military skills

Days later, early Thursday morning, Dorner allegedly opened fire on two LAPD police officers, wounding one, in the suburban city of Corona.

Roughly 20 minutes later, Dorner allegedly fired on two police officers, killing one and wounding another, in the nearby city of Riverside.

Since then, much of the manhunt for Dorner has focused in and around Big Bear Lake, after Dorner's pickup was found burning in the area. Officers trudged through fresh snow Saturday as they searched homes, knocking on doors and peeking in windows.

But as the search continued with no sign of Dorner, questions were raised about whether he had escaped the dragnet, possibly days earlier.

Arrest warrant

A federal arrest warrant affidavit said Dorner's burned-out truck was found near the property of a known associate in the Big Bear Lake area Thursday afternoon.

There has been no sign of Dorner since Thursday, and there has been speculation, based in part on the affidavit, that he has possibly crossed state lines into Nevada or made his way into Mexico.

Authorities say Dorner spent at least two days in the San Diego area after the shooting of Quan and her fiance.

Dorner's ID and some of his personal belongings were found Thursday at the San Ysidro Point of Entry at the U.S.-Mexico border, according to the affidavit.

Border patrol agents have been searching cars crossing into Mexico for signs of Dorner, while authorities have searched a home Dorner owned in Las Vegas and one owned by his mother in La Palma, California.

Two sailors reported Dorner, a former Navy lieutenant, approached them at the San Diego-area Point Loma Naval Base, and local police allege he attempted to steal a boat.

Even so, the focus of the manhunt remains on the San Bernardino Mountains, where the search has been slowed by heavy snowfall.

Search teams were aided by helicopters, snowcats and armored personnel carriers with snow chains.

On alert

Los Angeles-area police and several military installations have been on alert since the shootings, while authorities chase down unconfirmed sightings of the 270-pound, 6-foot Dorner.

In the manifesto and on a Facebook page, Dorner allegedly singled out as targets cartain officers and their families, who have been under guard since the shootings.

Beck said the LAPD is now guarding the families of more than 50 police officers. Officers guarding one house early Thursday shot and wounded two women who were driving a pickup similar to Dorner's, something Beck called a "tragic, horrific incident."

Beck said the shootings of Margie Carranza, 47, and her mother, 71-year-old Emma Hernandez, occurred a day after the manhunt for Dorner began, and that the officers were under enormous pressure.