“Just read his manifesto and look at his actions,” Riverside County District Attorney Paul Zellerbach said. “He’s trying to send a message, and it would be my belief that his message is not completed yet.”

On Monday, Zellerbach filed charges against Christopher Dorner for the murder of Riverside police Officer Michael Crain and the attempted murder of three other officers.

The manhunt for Dorner, 33, began last Wednesday when he was named the suspect in the Orange County killings of a former Los Angeles police captain’s daughter and her fiance the previous weekend. Hours after police announced they were looking for him, Dorner fired at two LAPD officers then ambushed the Riverside officers.

“By both his words and conduct, he has made very clear to us that every law enforcement officer in Southern California is in danger of being shot and killed,” Zellerbach said at a news conference that was guarded by four officers armed with rifles.

Police said Dorner wrote a lengthy manifesto that was posted to Facebook after the double murder. He vowed deadly revenge on those in the LAPD responsible for his firing years earlier, and their families. Police now are providing protection for some 50 families thought to be targets.

The search for Dorner was focused in the mountains near Big Bear Lake about 80 miles east of Los Angeles after his burned-out truck was found there last Thursday. Authorities are searching more than 30 square miles day and night in the ski resort area and checking on roughly 600 cabins.

Police and city officials believe a $1 million reward, raised from public and private sources, will encourage residents to stay vigilant. More than 700 tips had come in since the reward was announced.

“Now it’s like the game show ‘Who Wants to be a Millionaire,’” said Anthony Burke, supervisory inspector for the U.S. Marshals regional fugitive taskforce. “Instead of one contestant, we’ve got 100,000, and there’s only one question you have to answer. All they have to answer is where he’s at, and we can take it from there.”

The wide-ranging search has created unusually heavy traffic backups at California border crossings into Mexico, as agents are more closely inspecting each car. State police in Mexico’s Baja California were given photographs of Dorner and warned to consider him armed and extremely dangerous.

Authorities have obtained a no-bail arrest warrant, which allows Dorner to be apprehended anywhere, Zellerbach said.

Dorner was fired from the LAPD five years ago, when a department board determined that he falsely claimed another officer had kicked a suspect. Randal Quan represented him during the proceeding.

Quan’s daughter, Monica, and her fiance, Keith Lawrence, were found shot dead Feb. 3 in a car in the parking structure of their Irvine condominium. Last Wednesday, after discovery of the manifesto, Irvine police announced they were searching for Dorner.

Early Thursday in the Riverside County city of Corona, Dorner shot at two LAPD officers who had been dispatched to protect a possible target of Dorner’s, police said. One officer’s head was grazed by a bullet; the other was unharmed.

Minutes later, Dorner used a rifle to ambush two Riverside officers, killing one and seriously wounding another, authorities said. The slain officer was identified as Michael Crain, 34. The other officer’s identity was not released to protect his family.

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By Gillian Flaccus and Tami Abdollah. Abdollah reported from Los Angeles. Associated Press writer Elliot Spagat contributed to this report from San Diego. Follow Abdollah at http://www.twitter.com/LATams .