The burly Labrador retriever sticks out his wide snout to sniff the dirt and dusty air. He's clearly excited as he runs, yelping, through the high desert of California's Eastern Sierra region.

"Buster, go find!" Paul Dostie commands.

They are a team, the black Lab and the retired police officer. For years, they have worked together to unlock mysteries — to find the bodies of fighting men who fell long ago on foreign battlefields, or of victims of unsolved crimes or disappearances. In all, Dostie says that Buster's alerts have aided in the recovery of the remains of about 200 people.

"He's a one-in-a-million dog," Dostie says.

Maybe, but he's far from the only dog doing this kind of work. Increasingly, law enforcement investigators across the country are putting their faith in dogs like Buster to help find remains — bodies, bones and blood from the missing and the murdered. Cadaver dogs, as these specially trained canines are sometimes called, were used in searches after the terror attacks of Sept. 11, 2001, and to help find victims of natural disasters, such as Hurricane Katrina.

More recently, these dogs have helped convict some murder suspects, even when no body is found. Trainers and some forensic scientists say the dogs can detect human residue that's been left behind in a trunk, or on a blanket or tarp, or a temporary grave of some sort. In some cases, the dogs also help pinpoint areas where air and soil can be tested with increasingly sophisticated detection devices — though these methods have not been without controversy.

Proving what these dogs know isn't easy.

"If only Buster could talk," Dostie quips, as he works his dog through a wide patch of scraggly brush, about 50 miles east of Yosemite National Park.

Near an old mine shaft, Buster eventually zeroes in on a spot, then stops and barks with more urgency. "Show me, Buster!" Dostie shouts.

In his younger days, Buster would lie down on a spot like this to indicate an "alert." But having lost a leg to cancer, the 12-year-old canine now prefers to poke his nose in the direction of a particular spot in the dirt, or at a rock, or whatever has set off his nose.

As a reward, Dostie tosses Buster a blue rubber toy he's been holding behind his back while the dog searches. "Good boy," he says.

To the untrained eye, it might seem that Buster is simply barking for that toy.

But this routine has helped unearth the remains of everyone from crime victims to missing Americans lost in World War II battles in Europe and on the south Pacific island of Tarawa. Dostie and Buster travel to former war zones with History Flight Inc., a nonprofit foundation whose mission includes finding the tens of thousands of fallen American veterans whose bodies were never recovered.

Among others, Buster helped find Lt. Robert Fenstermacher, an Army Air Corps pilot whose plane crashed in Belgium after being shot down in 1944. Last year, his family gathered as he was laid to rest, nearly 70 years later, in Arlington National Cemetery.

"(Now) we can finally say to Robert: 'Welcome home. You served your country and family with honor and made us proud,'" the pilot's great-nephew, Robert Fenstermacher Jr., said at the funeral, as he thanked Buster, Dostie and other search volunteers.

History Flight volunteers also use ground-penetrating radar, historical records and witness accounts to pinpoint remains. The method has led to the recovery of 13,000 bones on Tarawa alone, most of them not yet identified, says Mark Noah, founder of History Flight.

Other searches are often much simpler — just the handlers and dogs, walking on foot, mile after mile to find a body. That was how Deborah Palman, now a retired specialist with the Maine Warden Service, and her German shepherd, Alex, found the body of a Canadian woman named Maria Tanasichuk in 2003. Police later determined she'd been shot in the head execution-style by her husband David Tanasichuk.

"We had worked so long for so many days — a lot of long, hard searches," Palman says. "You've sort of thrown yourself into numbness, and you convince yourself you're not going to find what you're looking for."

Then, during another long day trekking through a forest outside Miramichi, New Brunswick, Palman recalls how Alex ran to her as if to say, "Hey, come look at this. Follow me!"

Palman pulled back some brush and saw green fabric, and signs that a body was underneath.

"My pulse must have shot up over 200," she says.

That find was the break in the case that led to David Tanasichuk's conviction.

Local police departments have been reluctant to use the cadaver dogs for searches because their trainers are volunteers, but that's been changing, as the dogs' training has become more standardized in the last decade — and as they've helped solve more cases.

Labs and German shepherds are the most common breeds used for cadaver work. Like most of the dogs, Buster started young, though Dostie concedes that he ignored the pudgy puppy when his wife brought him home 12 years ago. She'd begged her husband to let her keep Buster — and then Dostie started noticing what a good nose the dog had.

The dogs are often trained at cemeteries and at specialized "body farms" that have decomposing bodies at various stages.

While humans, when alive, have individual scents, chemical reactions from decomposition are basically the same in every human, though those reactions — and the scent — change over time, forensic experts say.

When more than one dog has alerted independently in the same spot, some judges have been persuaded to allow cadaver dog evidence and testimony from the dogs' handlers, even if investigators haven't found the body.

In February, for instance, cadaver dog evidence helped convict a suburban Chicago man, Aurelio Montano, of killing his wife. She disappeared in 1990, and although her body was never found, investigators got a tip, years later, and dug up a rug at a horse farm on which more than one cadaver dog alerted. They contended that Montano had wrapped the body in the rug — also identified by his daughter as having once been in their home — and buried it. Those same investigators said Montano later exhumed his wife's remains and disposed of them in an unknown location.

The dogs' alerts on the rug, coupled with witness testimony, proved to be enough to convict Montano.

That sort of testimony has been less than effective in other cases, though.

In the high-profile 2011 Florida trial of Casey Anthony — accused of killing her young daughter — more than one cadaver dog alerted on the trunk of Anthony's car. Arpad Vass, then a senior research scientist with the Oak Ridge National Lab, testified that using air samples from the trunk, he had found high levels of chloroform, which can be found when a body breaks down. However, that finding was questioned by other witnesses and pundits, who said the science wasn't ready for primetime. And unlike Montano, Anthony was freed.

Cadaver dogs "are an incredible investigatory tool — no question about it," says Lawrence Kobilinsky, professor and chairman of the department of sciences at the John Jay College of Criminal Justice in New York. Certainly, he says, they can help uncover valuable evidence in criminal cases — a body, or bones or maybe clothing.

But he is among those who doesn't think the dogs' alerts and subsequent tests of soil and air where should be admissible in court, at least not yet.

"What we need to do is strengthen the science," Kobilinksy says.

And even in investigations, dogs alerting is often just the first step in what can be a lengthy, sometimes fruitless endeavor.

"Everybody thinks, you just dig a hole, but it's not always that obvious," says Vass, who is continuing to develop technology to help locate clandestine graves and to evaluate chemical markers associated with human decomposition. Often, he says, buried bodies create a "chemical plume" that runs downhill from a grave, making it difficult to find.

"Dogs," Vass says, "are just one tool in the toolbox."

Cost also can be a factor.

In Plumas County, California, Buster and two other dogs have alerted on an outdoor well on separate occasions. The well is near the home where 13-year-old Mark Wilson was living when he disappeared in 1967. Wilson was never found.

Plumas County Sheriff Greg Hagwood can't be sure the boy's body is in that well. But he thinks it's worth investigating, so much so that he asked for assistance from the Federal Bureau of Investigation, which has offered a forensics team.

The sheriff's department, however, still must foot the estimated $96,474 bill to excavate and restore the site, which is in the front yard of a home. That's no small amount of money in a county, once a busy logging and lumber hub, that's been hit by economic hard times.

With the funding turned down by the county board, the sheriff says he'll seek help from foundations or other sources.

"How can I justify not pursuing this?" he asks. "Well, you can't."

Buster, meanwhile, is still at work and may make another long trip to Tarawa. Noah, of History Flight, paid for the dog's cancer surgery, out of gratitude and to keep Buster's nose in the field.

"As long as he wants to work, he gets to work," Dostie says. "It's up to him."

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Martha Irvine can be reached at mirvine@ap.org or at http://twitter.com/irvineap