CARSON CITY, Nev.—Larry and Marty Hall had two massive bull elk sighted in their rifle scopes. A cracking boom from one gun, then another, echoed across the rugged landscape along the Nevada-Idaho line.

One animal, crowned with a majestic six-by-six antler rack, was dead. The other, a six-by-four, was mortally wounded but alive.

Neither Larry nor his son Marty had a tag to hunt elk.

But Larry’s longtime buddy, Frank Koski, did. Koski took back his rifle from Larry and finished off the wounded bull. The trio and Frank’s two sons, John and Andrew, then hauled out the now-tagged animal with an ATV, leaving the other to rot.

Across the way, other hunters had been scouting the same elk that day. They knew what they witnessed Nov. 6, 2010 wasn’t right.

So began a yearlong poaching investigation that involved agencies from three states, sophisticated DNA analysis on frozen meat in household freezers and blood splotches lifted from an ATV tire thousands of miles from the crime scene.

Old fashion gumshoe and a black lab with a fine-tuned nose helped seal the case.

“It’s the same as a homicide investigation,” said Rob Buonamici, law enforcement chief for the Nevada Department of Wildlife. “We have to literally prove the same elements as a homicide. Except we can’t go to the mountain and talk to the elk that are left and ask them who did it.”

Over the past three decades or so, poachers have become more technologically advanced—using night vision goggles, trail cameras, satellite mapping and two-way radios, among other tools. That means wardens have had to evolve as well, finding ever new and creative ways of sleuthing.

Buonamici recalled a case in the early 1980s where he took a dead deer to a veterinarian, who X-rayed the bullet path. Buonamici poked a stick into the wound channel to show the angle of impact and prove the kill shot came from someone in a pickup truck.

These days, DNA is just as critical in animal crime investigations as it is solving human crimes.

“Our lab has been doing this since the mid-1990s,” said Elizabeth Wictum at the animal forensics lab at the University of California, Davis, where DNA collected in the Nevada case was analyzed. The world’s largest animal forensic lab, operated by the U.S. Fish and Wildlife Service, opened in 1989 in Ashland, Ore.

Buonamici predicted in the not-to-distant future, DNA techniques will allow biologist to pinpoint the region an animal came from—and nab hunters who have a tag for one area but kill their bounty in another.

“It’s coming,” he said.

In the Nevada case, game wardens took blood and tissue samples from the scene and the carcass left behind. From witness accounts, investigators were able to identify the five suspects after searching through the state hunting tag database.

“One person saw Marty Hall coming out of the trees, and when he got on a four-wheeler he didn’t have a rifle anymore,” said Fred Esparza, NDOW game warden and lead investigator.

That December, search warrants were issued for five different homes, four in Nevada and Larry Hall’s home in Franktown, Colo., a small community south of Denver. Samples were taken from frozen meat in freezers, and Colorado wildlife officers lifted a blood sample from an ATV tire.

But it would be another six months before investigators found the missing gun used to shoot the big elk that was left to rot. That break came with the help of a four-legged officer named Pepper, trained to sniff out weapon odors like gun oil and gun powder.

Owned and handled by Jim Stirling, senior conservation office with the Idaho Department of Fish and Game, the elk caper was one of Pepper’s first assignments.

On June 10, 2011, the sharp-nosed dog found the weapon during the spring thaw, hidden under sagebrush.

“This gun was buried under feet of snow for six months before I was even able to get access to this area,” Esparza said.

Forensic testing confirmed bullets fired from the weapon Marty Hall had ditched matched the bullet that killed the elk.

Larry Hall, 65, and Marty Hall, 45, pleaded guilty last week to killing or possessing a bull elk without a tag. Larry Hall was ordered to pay more than $8,000 in fines; his son was assessed more than $3,500 in fines and forfeited a Yamaha Kodiak ATV.

Frank Koski, 86, and John Koski, 50, pleaded no contest in November to gross misdemeanors of possessing an elk without a tag. Each was fined more than $3,000. Last July, Andrew Koski, 48, pleaded guilty to hindering a game warden and was fined $632. Each also could face revoked hunting privileges in Nevada and more than 30 other states, under a multi-state compact

Wildlife experts and others point out that the rigorous, detailed work involved solving such cases is worth the effort, though there’s much more to do.

“We hear from state wildlife agencies that estimate as few as 1 percent to 5 percent of poaching incidents actually come to their attention,” said Elise Traub, spokeswoman for the Humane Society of the United States. She points to an undercover taxidermy shop set up by the Missouri Department of Conservation. Between 2008 and 2010, 62 percent of the wildlife—from deer and turkey to fish—brought in for mounting had been killed illegally.