LOS ANGELES: Detectives were pursuing some 600 clues in their hunt for an ex-police officer suspected of killing three people, Los Angeles police officials said on Monday, a day after a $1 million (Dh3.67 million) reward was posted for information leading to the wanted man’s capture.

Christopher Dorner, 33, has not been spotted since early Thursday, when he is accused of ambushing two policemen at a red light in Riverside, 60 miles east of Los Angeles. One of those officers was killed, the other wounded.

That confrontation came shortly after the former Los Angeles police officer and US Navy veteran is suspected of exchanging gunfire with police in nearby Corona, wounding one officer.

Riverside prosecutors formally charged Dorner on Monday with one count of first-degree murder and three counts of attempted murder in connection with those shootings and said they had issued a “no-bail” arrest warrant for the fugitive.

Riverside County District Attorney Paul Zellerbach told a news conference that the evidence already amassed against Dorner was strong enough that “there was no reason to withhold filing of charges” against him.

“This individual, by both his words and his conduct, has made it very clear to all of us that every law enforcement officer in Southern California is in danger of being shot or killed,” Zellerbach said.

Aside from several false sightings, the search for Dorner has centred on the San Bernardino Mountains northeast of Los Angeles, where his truck was found burning on a fire road near the ski resort community of Big Bear Lake.

That effort has not been abandoned, LAPD spokesman Lieutenant Andrew Neiman said, but detectives were also busy following up hundreds of clues and tips from the public in hopes that one of them would lead them to the fugitive.

“As of 6am this morning, our investigators were working on over 600 clues, and I’m sure that number has increased since then,” he said.

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Dismissing speculation that Dorner’s four-day silence may suggest he had taken his own life, Neiman said: “We are operating on the premise that he is still out and about and we are going to find him.”

Police officials urged Southern Californians to call a tip line with any information on Dorner’s whereabouts. But they said anyone who actually spots him in person should call 911 immediately.

Los Angeles Police Chief Charlie Beck has said that the $1 million reward, raised from private donations, police unions, businesses and local governments, the largest sum ever offered in Southern California in a criminal investigation.

Beck has also described the manhunt for Dorner as the most extensive ever mounted in the Los Angeles area.

“This is a man who has targeted those who we entrust to protect the public. His actions cannot go unanswered,” Beck told a news conference on Sunday.

A manifesto posted on Dorner’s Facebook page last week claimed he was wrongly terminated from the LAPD in 2008 and vowed to seek revenge by unleashing “unconventional and asymmetrical warfare” on police officers and their families.

More than a week ago, he was named as a suspect in the slayings of a campus security officer and his fiance, the daughter of a retired Los Angeles police captain that Dorner’s manifesto blames for his dismissal.

The couple, Keith Lawrence, 27, and Monica Quan, 28, were found shot dead eight days ago in their car on the top level of a parking structure in the city of Irvine, south of Los Angeles.

Dorner had ended his military service two days earlier, and the Navy has not disclosed the circumstances of his discharge.

Beck announced on Saturday a reopening of the inquiry into Dorner’s firing to “reassure the public that their police department is transparent and fair”.

The LAPD also has opened an investigation into an incident in which two women were wounded when apparently skittish officers opened fire on a pickup truck resembling Dorner’s. The two women were delivering newspapers when they were shot.