SALT LAKE CITY (AP) – Federal authorities in charge of the biggest U.S. bust of artifact looting and grave-robbing are targeting more suspects ranging from those who do the digging to wealthy buyers in the lucrative black market of ancient Southwest relics.

Twenty-five people have already been charged after a long-running sting operation involving a bounty of artifacts taken from federal and tribal lands in the Four Corners region.

More arrests are likely, according to federal officials. Among the next targets could be wealthy collectors who fuel the underground trade.

“It’s fair to say the investigation is looking at all levels, from diggers and dealers to high-end collectors,” said Carlie Christensen, an assistant U.S. attorney for Utah.

The case was the first to deeply penetrate the murky world of Native American artifacts trafficking, relying on a well-connected artifacts dealer-turned-undercover operative.

The man was equipped to provide federal agents with wireless video feeds from homes and shops where he wheeled and dealed over artifacts, ultimately spending more than $335,000 on bowls, stone pipes, sandals, jars, pendants, necklaces and other items.

He was paid $224,000 for the undercover work over 21/2 years, according to search warrant affidavits describing his work.

The informant gave federal officials a rare insider’s view of the illegal artifacts trade, recording a parade of suspects as they described their methods in astonishing frankness.

They discussed digging in camouflage or by moonlight, knowing when a park ranger takes his days off, and looting in spring when the dirt softens up and before the heat of summer.

One suspect said he scouted for ruins in a fly-over and followed up with a 10-mile hike. Another dug fresh holes on his property in case “someone comes asking” about where his artifacts came from, the documents say.

Yet another boasted that in a 1986 raid, federal agents took 32 of his pots, but overlooked a hidden safe and the most damning evidence – a ledger of a lifetime of trading that named people he dealt with.

At another point, the informant watched a suspect dig up an ancient burial site and kicked out a skull on the third shovelful.

Authorities could not make a case this large without someone on the inside, U.S. Attorney Brett Tolman said.

“Without a source that has been in this and knows the individuals involved, it would be very hard to get a clear or large picture,” he said.

Practically every defendant offered in secret recordings that the objects they acquired had been illegally taken from ruins on government or tribal lands across Arizona, New Mexico, Utah and Colorado.

The exquisite pieces, typically a thousand years old, quickly disappear into living rooms, lucrative underground markets or the hands of wealthy private collectors.

The investigation broke open in early June with early morning raids on a dozen rural Utah homes. Other defendants were arrested or surrendered in Colorado and New Mexico.

In short order, two of the defendants – one a prominent doctor, the other an unemployed salesman – committed suicide. The Utah physician, Dr. James Redd, died by carbon monoxide poisoning inside his Jeep on his ranch. His wife and daughter quickly pleaded guilty to separate charges.

The Santa Fe, N.M., salesman, Steve Shrader, traveled to Illinois to pay his mother a visit and then shot himself in the chest behind an elementary school.

The rest of the defendants have pleaded not guilty. A status conference for their lawyers is scheduled for Aug. 18.

Authorities have seized truckloads of artifacts and are pursuing leads. The investigation is already having a chilling effect on the market, and it could drive the criminal element deeper underground, said Larry Shackelford, the Bureau of Land Management’s lead law enforcement agent in Utah.

At least one major artifacts dealer who wasn’t caught up in the dragnet says he’s still expecting a knock on the door from federal agents.

The investigation has given a black eye to every legitimate dealer, said Walter Knox, the owner of Fort Knox Antiquities, an upscale gallery in Scottsdale, Ariz.

“I’m sure I’ll be ‘visited’ eventually,” Knox said. “I haven’t been yet, but I’m sure it’s a matter of time.”

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