Police were awaiting forensic analysis to confirm charred remains found inside the cabin in the wooded hills of the San Bernardino National Forest were those of 33-year-old Christopher Dorner.
Authorities including Los Angeles Mayor Antonio Villaraigosa said the man who had barricaded himself inside the cabin was almost certainly Dorner.
He said: "There's a sigh of relief. Almost everybody believes it is him, but at this point we're not absolutely sure.
He cautioned it could be days, maybe even weeks, before there is final confirmation Dorner was dead.
Dorner had been the subject of a six-day manhunt across southern California.
He is believed to have made his last stand in the cabin, where a gun battle ended in the death of a sheriff's deputy and the wounding of another deputy.
Dorner is suspected of killing another three people.
An angry manifesto posted last week on Dorner's Facebook page claimed he had been wrongly dismissed from the Los Angeles Police Department (LAPD) in 2008.
He vowed to seek revenge by unleashing "unconventional and asymmetrical warfare" on officers and their families.
It has been reported that Tuesday's climax to the manhunt began when two housekeepers encountered a man believed to have been Dorner inside a vacant cabin near the ski resort community of Big Bear Lake.
They surprised the suspected fugitive, who tied them up and then took off in a purple Nissan parked near the cabin.
One of the women is understood to have freed herself and called police.
State game wardens spotted the vehicle and gave chase.
The suspect crashed the car, then commandeered a truck at gunpoint from another motorist, said Lieutenant Patrick Foy of the state Fish and Game Department.
Mr Foy said the suspect fired at the wardens from the window of the truck and one of the wardens stopped his truck and returned fire with a high-powered rifle. He said he did not know if the suspect had been hit.
The lieutenant said officers got close enough during the chase to recognise the driver as Dorner before he abandoned the truck and fled into the woods to the cabin.
During a lull in the eventual shootout, the cabin caught fire and was engulfed in flames.
Dorner's last confirmed encounter with authorities was on Thursday, when police said he ambushed two policemen at a traffic light in Riverside, about 60 miles east of Los Angeles.
One officer was killed and the other wounded.
The former US Navy officer is also suspected of having exchanged gunfire on Thursday with police in nearby Corona. One officer was wounded.
The hunt for Dorner began last Wednesday when police identified him as a suspect in the slayings of a campus security officer and his fiancee, the daughter of a retired Los Angeles police captain.
In his manifesto on his Facebook page, Dorner blamed the captain for his dismissal from the LAPD.