Are police using drones in the manhunt for Christopher Dorner?

According to a report by a British newspaper, they are. On Sunday, the Express quoted a "senior police source" who said the "thermal imaging cameras the drones use may be our only hope of finding him—on the ground, it's like looking for a needle in a haystack."

Dorner, the 33-year-old former naval and LAPD officer turned triple-murder suspect, has been at the center of a massive manhunt stretching from the San Bernadino Mountains—where his burned-out pickup truck was found last week—to the Mexican border.

In a manifesto posted online earlier this month, Dorner promised "unconventional and asymmetrical warfare" against the LAPD, which fired him in 2008. On Saturday, actor Charlie Sheen—who was mentioned in Dorner's online manifesto—released a video pleading with the accused killer to call him.

According to the paper, a pair of cryptic statements by law enforcement and U.S. Border Patrol officials back their source's drone claim.

“We are using all the tools at our disposal," Riverside Police Chief Sergio Diaz responded when asked if drones were being used in the hunt for Dorner.

Ralph DeSio, a spokesman for the U.S. Customs and Border Patrol, added: "This agency has been at the forefront of domestic use of drones by law enforcement. That’s all I can say at the moment.”

As Gizmodo.com noted, it wouldn't be the first time drones were used in tracking fugitives on U.S. soil.

From Time:

In June 2011 a county sheriff in North Dakota was trying to track down three men, possibly carrying guns, in connection with some missing cows. He had a lot of ground to cover, so—as one does—he called in a Predator drone from a local Air Force base. It not only spotted the men but could see that they were in fact unarmed. It was the first time a Predator had been involved in the arrest of U.S. citizens.

But it would come at a time when U.S. drone use--both domestically and abroad--under President Barack Obama has come under increased scrutiny. Last week, Sen. Bob Corker, the top Republican on the Senate Foreign Relations Committee, told Yahoo News that the White House's deadly drone war against suspected extremists, including Americans overseas, may not be legal.

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On Saturday, police conducted a door-to-door search for Dorner in Big Bear Lake, Calif., but snowfall hampered their efforts in the surrounding mountains.

On Sunday in Los Angeles, an increased police presence was seen at the Grammy Awards, which some thought Dorner might target. In Northridge, Calif., a home improvement store was evacuated after a report of a possible Dorner sighting, hours after the LAPD announced a $1 million reward for information leading to his arrest.

"This is the largest local reward ever offered, to our knowledge," Los Angeles Police Chief Charlie Beck said at a news conference. "This is an act of domestic terrorism. This is a man who has targeted those that we entrust to protect the public. His actions cannot go unanswered."

Meanwhile, the U.S. Border Patrol has stepped up security, screening vehicles to prevent Dorner from fleeing the country into Tijuana.