Los Angeles area police have launched a huge manhunt for a sacked officer who is suspected of killing three people, including a former colleague.

Christopher Dorner, 33, is alleged to have gunned down a policeman and wounded two others on Thursday morning.

He is also wanted over the shooting deaths of a couple at the weekend.

Mr Dorner is said to have implicated himself in a "manifesto" he wrote, that made threats against several people, including Los Angeles police employees.

The rambling essay also warns of "unconventional and asymmetrical warfare to those in LAPD uniform whether on or off duty".

Officials have issued a statewide "officer safety warning" and assigned more than 40 protection details to potential targets.

Mr Dorner, a US Navy reservist, was with the police department between 2005-08, but lost his job for making false statements.
Officers 'ambushed'

"Of course he knows what he's doing - we trained him," Los Angeles chief of police Charlie Beck told reporters on Thursday. 

"It is extremely worrisome and scary, especially to the police officers involved."

Mr Dorner is accused of killing Monica Quan, 28, and her fiance Keith Lawrence, 27, on Sunday night.

They were found with multiple gunshot wounds in their vehicle in the car park of their flats in Irvine, California.

Quan's father, a retired policeman, had represented Mr Dorner before a disciplinary tribunal that ruled against the suspect at the time of his dismissal.

Officials say Mr Dorner also shot at two officers in the early hours of Thursday morning in the city of Corona, east of Los Angeles. One of the officers was grazed.

The Los Angeles Times reports that those officers were protecting a possible target of Mr Dorner.

Later, two policemen were ambushed in their patrol car at a red light in Riverside, a nearby town.

One officer was killed and the other was undergoing surgery. Riverside officials said the ambushed officers had not been actively looking for the suspect. 

On Thursday morning, jittery Los Angeles police mistakenly fired on a pickup truck they thought was similar to one used by Mr Dorner.

Two women in the vehicle were injured. One was in a stable condition with two gunshot wounds and the other was being released after treatment.

It is understood that the officers had been guarding someone or something targeted in the suspect's manifesto.

Police said earlier that an LAPD badge and identification belonging to Mr Dorner had been found by a citizen near San Diego's airport.

San Diego police said a man matching the suspect's description had tried to steal a boat from one of the city's marinas. When the boat would not start, that person tied up an 81-year-old man on board and fled.

The authorities have appealed to the public for help locating Mr Dorner, but warn that he should not be approached.

"He's already demonstrated he has a propensity for shooting innocent people," said LAPD commander Andrew Smith.

Mr Beck said that Mr Dorner has access to multiple weapons, including an assault rifle.
'Necessary evil'

The FBI are said to be assisting with the case and Nevada police are also on alert, as the suspect owns a house nine miles (14.5km) from the Las Vegas Strip.

Authorities said the suspect may be driving a blue 2005 Nissan Titan pickup truck. He was last known to be living in La Palma, California.

According to court documents, Mr Dorner was fired in 2008 after making a complaint against his field training officer, saying she had kicked a suspect, a schizophrenic man with severe dementia, during an arrest.

The alleged victim's father gave testimony at a court of appeal that supported Mr Dorner's claim.

Mr Dorner's "manifesto" extends for more than 11,000 words and contains a number of allegations against former colleagues, together with embittered reflections on his childhood.

In it, he says he expects to be vilified by the LAPD, but that "unfortunately, this is a necessary evil that I do not enjoy but must partake and complete for substantial change to occur within the LAPD and reclaim my name".

The profanity-peppered rant finishes with praise for a range of public figures and celebrities, from New Jersey Governor Chris Christie to the actor Bill Cosby.