Earlier, as President Obama and the Beltway establishment were preparing for the annual State of the Union address - which featured a call for action to reduce gun violence - millions tuned in to watch the standoff unfold on live television against a darkening California backdrop of thick evergreens and deep snow.
A SWAT team surrounded the cabin and using an armored vehicle, broke out the cabin windows, a law-enforcement official told the Associated Press. The officers pumped gas into the cabin and blasted a message over a loudspeaker: "Surrender or come out."
The armored vehicle then tore down each of the cabin's four walls, like peeling back the layers of an onion, the official said.
Approaching officers heard a single gunshot and soon saw flames shooting from the building.
The tense cabin standoff between Dorner and the authorities appeared to be the climax of a nine-day drama that started on Feb. 3 - Super Bowl Sunday - when the fired ex-cop carried out revenge killings against two people with family ties to the L.A. police.
The tangled chain of events dates back to 2008, when the now-32-year-old Dorner - an ex-Navy reservist who'd served in Bahrain - was fired from the L.A. police department after his brief stint as an officer.
Although reports said that Dorner's entire time on the force was a rocky one, the specific spark for his firing was an accusation that Dorner was lying when he claimed that his partner had kicked a mentally-ill suspect whom they were arresting.
Dorner's anger clearly seethed over the four years since he lost his dismissal hearing, and came out in a lengthy Facebook manifesto in which he complained about racism - both in his young life and as an L.A. officer - and pledged a campaign of "unconventional and asymmetrical warfare" against as many as 20 current and former officers and their families.
The Southern California killing spree began when 26-year-old Monica Quan - daughter of the former Los Angeles police captain who represented Dorner at his disciplinary hearing - was found dead alongside her fiancee in a parked car in Irvine.
The next alleged encounter involving Dorner took place four days later, after his manifesto had been published and he was named as a murder suspect. After a shootout with two officers, Dorner allegedly ambushed two other cops in Riverside, Calif., killing one and critically wounding the other.
That night, a burning Nissan pickup truck believed to be Dorner's was discovered on a remote fire trail near Big Bear Lake, about an hour's drive from Los Angeles - focusing the manhunt in that snowy and mountainous area.
Around 12:20 p.m. Pacific time on Tuesday, deputies got a report of a stolen vehicle, authorities said. The location was directly across the street from where law enforcement had set up their command post on Thursday and not far from where Dorner's burned-out pickup was abandoned.
About 25 minutes later, the car was stopped by two Fish and Wildlife officers who exchanged gunfire with a suspect who matched Dorner's description.
Then, after Dorner retreated to a nearby vacation cabin in the woods, there was a second exchange with San Bernardino County deputies, two of whom were shot. One died and the other was expected to live after undergoing surgery.
"We're heartbroken," Big Bear Lake Mayor Jay Obernolte said of the deputy's death and the wounding of his colleague. "Words can't express how grateful we are for the sacrifice those men have made in defense of the community, and our thoughts and prayers are with them and their families."
Over the course of the afternoon, hundreds of armed SWAT-team members surrounded the small cabin and authorities begged news helicopters to cease showing live pictures of the scene.
Around 3:30 p.m. California time - 6:30 here - TV coverage resumed and showed orange flames engulfing the cabin as black smoke rose into the chilly mountain air.
Despite concerns that the killer might have escaped, all signs soon pointed to the likelihood that no one survived the inferno. By then, the news networks were switching their focus 3,000 miles away to Washington.
It was time for President Obama to put his official stamp on the state of the union.
"Police chiefs are asking our help to get weapons of war and massive ammunition magazines off our streets," Obama said, "because they are tired of being outgunned."
The Associated Press contributed to this article.
On Twitter: @Will_Bunch