IRVINE, Calif. — A $1 million reward for a fugitive ex-police officer wanted in the slayings of three people took authorities to a San Fernando Valley home improvement store but so far prompted no credible leads in the search for Christopher Dorner.

The manhunt for him, coupled with the need for added security at Sunday’s Grammy Awards, left the ranks of the Los Angeles Police Department stretched thin. A tactical alert began Sunday afternoon and remained in effect Monday for all city officers, which means they’re staying on duty beyond their shifts.

Besides responding to the usual calls for service, police have been protecting dozens of families in the area considered targets based on Dorner’s Facebook rant against those he held responsible for ending his career with the LAPD five years ago.

Among those Dorner, 33, is suspected of killing is a Riverside police officer, and on the fourth day of the manhunt, authorities put up a $1 million reward for information leading to his capture.

“Our dedication to catch this killer remains steadfast. Our confidence remains unshaken,” Los Angeles Mayor Antonio Villaraigosa said at a news conference alongside police chiefs and mayors from Irvine and Riverside. “We will not tolerate this reign of terror.”

Several tips came in within a few hours after the award announcement, including a reported Dorner sighting that had police surrounding and evacuating a Lowe’s Home Improvement store in LA’s San Fernando Valley, police spokesman Gus Villanueva said. A search of the store yielded no evidence that Dorner was there or had been there.

After days without resolution, Dorner’s fugitive status caused concern among some and downright fear among others in Irvine, an upscale community that the FBI consistently ranks among the safest cities in the U.S.

“If he did come around this corner, what could happen? We’re in the crossfire, with the cops right there,” said Irvine resident Joe Palacio, who lives down the street from the home surrounded by authorities protecting a police captain mentioned in Dorner’s posting.

“I do think about where I would put my family,” he said. “Would we call 911? Would we hide in the closet?”

The neighborhood has been flooded with authorities since Wednesday. Residents have seen police helicopters circle and cruisers stake out schools. Some have responded by keeping their children home. Others no longer walk their dogs at night.

Police also were looking into a taunting phone call to the father of the woman they believe Dorner killed last week.

Two law enforcement officers who requested anonymity because of the ongoing investigation told The Associated Press they are trying to determine whether Dorner made the call telling retired police Capt. Randal Quan that he should have done a better job protecting his daughter.

The bodies of Monica Quan and her fiance were found shot dead last Sunday in Irvine, marking the start of the high-profile case.

Things escalated early Thursday, when police say Dorner got into a shootout with police in Corona, grazing an LAPD officer’s head with a bullet before escaping. Authorities believe he then used a rifle to ambush two Riverside police officers, killing one and seriously wounding the other.

Police had withheld the names of victims both living and dead victims because of fears of Dorner targeting their families, but on Sunday the Riverside Police Department released the name of the officer killed, 34-year-old ex-Marine and 11 year department veteran Michael Crain.

The Anaheim native and father of two will be buried at Riverside National Cemetery on Wednesday.

Riverside police Chief Sergio Diaz said police had hoped Dorner would be in custody by now, but they decided to proceed with the identification and public memorial.

“We’re not going to fail our officer and our hero,” Diaz said Sunday. “We’re going to bury him.”

After Thursday’s shootings in Corona and Riverside, officers in Torrance twice mistakenly identified people in their search for Dorner.

A lawyer for the driver of a pickup peppered with police bullets said police were reckless. Surfer Dan Perdue was driving to the beach early Thursday when his Honda Ridgeline was stopped by officers guarding the home of a law enforcement official targeted by Dorner.

The pickup resembled Dorner’s Nissan Titan. After driving away, the Ridgeline was hit by a squad car.

Perdue attorney Robert Sheahen tells the Daily Breeze of Torrance (http://bit.ly/12F0uON ) the pickup spun around and officers began shooting. Perdue wasn’t wounded.

A police department statement says Perdue’s vehicle was suddenly leaving the area and officers on heightened alert took appropriate measures.

The shooting was blocks from the mistaken identity LAPD shooting of two women delivering newspapers.

The manhunt continued Monday in the San Bernardino mountains near the ski resort town of Big Bear, where authorities found Dorner’s burned out pickup truck Thursday. Police have since said they discovered weapons and camping gear inside the vehicle.

The search scaled down as the weekend went on, but a helicopter with heat-seeking technology scanned the area as two-dozen officers went back to some of the 600 cabins they earlier visited door to door.

LAPD Chief Charlie Beck said despite the dwindling search, there was not another area that appeared more likely than Big Bear where Dorner might be, saying the suspect’s chances to plan beforehand may have helped him remain elusive.

“We have nothing currently better, Beck said at Sunday’s news conference.

Police and city officials believe the $1 million reward, raised from both public and private sources, would give them better options.

Beck said the money, believed the biggest reward in local history, was not difficult to pull together.

“It was amazingly, amazingly easy,” he said.

The chief said the case is distinct from most that offer rewards for fleeing fugitives because police strongly believe Dorner would strike again if given the chance.

“This is not about catching a fugitive suspect, it’s about preventing a future crime, most likely a murder,” Beck said. “This is an act, make no mistake about it, of domestic terrorism.”

He deflected questions about whether the reward applied whether Dorner were dead or alive, calling the phrase “ugly” and saying he hoped no one else was injured in the ordeal, including the suspect.

With little apparent evidence pointing to Dorner’s whereabouts, worrisome questions emerged: How long could the intense search be sustained? And, if Dorner continues to evade capture, how do authorities protect dozens of former police colleagues whom he has publicly targeted?

LAPD Cmdr. Andrew Smith said the department has deployed 50 protection details to guard officers and their families who are deemed targets in Dorner’s manifesto.

“It can’t be one guy with a gun in a living room,” Smith said, suggesting that more officers would be necessary to keep families safe.

The department, however, is looking for alternatives if the search for Dorner stretches on, whether it’s reducing the numbers of officers or something else, he said.

There were no plans to reduce protections until Dorner was in custody, Los Angeles police Sgt. Rudy Lopez said.

As long as Dorner’s whereabouts are unknown, the police department must provide protection to those named in his rant, said Chuck Drago, a Florida-based police consultant.

“We realize it costs money and it gets expensive, but this is as clear of a threat as you can get,” he said. “We know that if he’s able to get to these targets then he’s probably able to hurt them. The money is always an issue but not when it’s somebody’s life at stake.”

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Associated Press writer Andrew Dalton in Los Angeles contributed. Abdollah can be reached at http://www.twitter.com/LATams.