San Bernardino Sheriff John McMahon said police could not yet identify the remains as those of Christopher Dorner.
But "we believe this investigation is over at this point", he said.
Dorner is accused of killing three last week and engaging in a gun battle with officers as they closed in on Tuesday.'War zone'
The manhunt ended on Tuesday afternoon, after police received word that a man matching Dorner's description had stolen a vehicle in the area of Big Bear Lake, a ski resort 80 miles (130km) east of Los Angeles.
Officers pursued the suspect, who took refuge in the cabin on a snowy, wooded mountain. The suspect fired on police as they surrounded him, in a scene Sheriff McMahon likened to a war zone.
"The rounds kept coming but the deputies didn't give up," he said at a news conference on Wednesday. "Our deputy sheriffs are true heroes."
In suicides, says Jack Digliani, a police psychologist with the Loveland, Colorado Police Department, police officers are more likely to leave a note than the general population. Dorner left a manifesto, sent to a media station before he allegedly committed his first crimes.
"In many cases, a manifesto reads like a suicide note," says Digliani. Dorner's lengthy manifesto, he said, had similar hallmarks, including a section thanking those who helped him. The manifesto, says Digliani, also offers insight into how Dorner could have turned from cop to criminal.
"It's [presented as] a righteous cause," he says. "It's two-fold. One is to change the LAPD, the other is to reclaim his name and his reputation. This is the avenger/crusader perspective: 'I don't want to do this, but it's the only way to accomplish the goal.'"
In the fight, Detective Jeremiah MacKay was shot and later died from his wounds. Another officer, Deputy Sheriff Alex Collins, was shot and has undergone surgery in hospital.
During the gun battle police shot tear gas canisters into the building in an effort to drive Dorner out.
Shortly afterwards, police heard a single gunshot as fire began to spread through the cabin.
It is not clear how the blaze started, and Sheriff McMahon said officers had not "intentionally" set fire to the cabin.
But he acknowledged the pyrotechnic tear gas canisters "generate a lot of heat".
"We introduced those into the residence and a fire erupted," he said.
"The pyrotechnic-type canisters are commonly referred to as burners."
Forensic tests will determine if the charred remains found in the razed cabin after Tuesday night's siege are those of Dorner, Sheriff McMahon said.Revenge
Dorner, a 33-year-old former Navy reservist, is suspected of killing three people in a spree across southern California last week, including a policeman.
Footage showed the fierce gunfight that took place at the cabin
During the manhunt police guarded about 50 families, many belonging to former Los Angeles Police Department (LAPD) colleagues against whom Dorner had vowed revenge for allegedly ruining his career.
He was fired for making false statements, after lodging a complaint against his field training officer, saying she had kicked a suspect during an arrest.
His killing spree began on 3 February when he shot dead the daughter of a former police captain who represented him at his police disciplinary board, and her fiance.
Dorner apparently believed the woman's father, Randal Quan, had not defended him adequately.
Police say he shot and killed a Riverside, California policeman in an ambush on 7 February.
In an online manifesto, Dorner, who was black, suggested that racism was still rife in the LAPD.
It was an unwelcome allegation for a department that overhauled itself after the notorious police beating in 1991 of a black man, Rodney King.
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