A massive manhunt was under way in Southern California for a sacked policeman accused of three murders, who declared war on law-enforcement officers and their families in a rambling internet manifesto.
Protection teams were dispatched overnight to guard uniformed officers and their families, scores of officers set up lines of defence outside the fortress that is the Los Angeles Police Department headquarters, and motorcycle officers were ordered to retreat to the safety of patrol cars.
Overnight, police swarmed the mountains surrounding a California ski area for Christopher Dorner, who is said to be heavily armed.
The bloodshed attributed to Dorner, 33, began with the weekend slayings of a university safety officer and his fiancée, Monica Quan, 28.
She was the daughter of a retired Los Angeles police captain who represented Dorner in disciplinary action that led to his firing in 2008. Quan and her fiancé were found dead in Irvine, 64 kilometres south of Los Angeles.
The violence escalated on Thursday with the fatal shooting of a police officer in Riverside and the wounding of two others.
Later, two women delivering newspapers were shot and wounded by police officers who mistook the Honda truck they were driving for the one identified as belonging to the gunman, a grey Nissan.
Dorner's truck was later found burning in the snow near the mountain resort of Big Bear Lake, 129 kilometres northeast of Los Angeles. Investigators found tracks leading away from the truck, but they did not lead to the suspect.
Television networks broadcast footage showing armed police apparently fanning out across a mountain slope, although the LAPD quickly asked broadcasters not to show live footage, to avoid giving Dorner help if he was watching.
Dorner, who joined the US Navy in 2002 and the LAPD in 2005 and was a naval reservist until yesterday, had posted his grievances on Facebook.
The 6,000-word manifesto was bristling with anger and explicit threats, naming two dozen police officers he intended to kill.
Los Angeles police chief Charlie Beck said: "This is a vendetta against all of Southern California law enforcement and it should be seen as such.
"He knows what he's doing. We trained him. He was also a member of the armed forces. It is extremely worrisome and scary, especially to the police officers involved."
Dorner was presumed to be armed with multiple weapons, including an assault rifle, Beck said, although his manifesto suggested that he might be more heavily armed.
"Do not deploy airships or gunships. SA-7 Manpads will be waiting," Dorner wrote, referring to a portable missile system.
"The violence of action will be high. I will bring unconventional and asymmetrical warfare to those in LAPD uniform whether on or off duty.
"The attacks will stop when the department states the truth about my innocence," read the document, which had been taken down from Facebook.
Dorner was dismissed after being charged with making false statements about his training officer, who he alleged had kicked a suspect. A review board ultimately found Dorner guilty. He sued the department, but both the trial court and an appellate court upheld his termination.
FBI agents staked out a home in Orange county where neighbours said Dorner's mother lived. Neighbours said they had seen Dorner on and off since 2006. They all said he was cordial and approachable. "I don't expect to see him anymore, because I know that this is a hot area for him," said Ike Gonzalez.
Agence France-Presse, Reuters, The New York Times