KRUGER NATIONAL PARK, South Africa » They definitely did not look like ordinary big-game hunters, the stream of slender young Thai women who showed up on the veld wearing tight blue jeans and sneakers.

But the rhinoceros carcasses kept piling up around them, and it was only after dozens of these hulking, relatively rare animals were dead and their precious horns sawed off that an extravagant scheme came to light.

The Thai women, it ends up, were not hunters at all. Many never even squeezed off a shot. Instead, they were prostitutes hired by a criminal syndicate based 6,000 miles away in Laos to exploit loopholes in big game hunting rules and get its hands on as many rhino horns as possible — horns that are now literally worth more than gold.

"These girls had no idea what they were doing," said Paul O’Sullivan, a private investigator in Johannesburg who helped crack the case. "They thought they were going on safari."

The rhino horn rush has gotten so out of control that it has exploded into a worldwide criminal enterprise, drawing in a surreal cast of characters — not just Thai prostitutes, but also Irish gangsters, Vietnamese diplomats, Chinese scientists, veterinarians, chopper pilots, antiques dealers and recently a U.S. rodeo star looking for a quick buck who used Facebook to find some horns.

Driven by a common belief in Asia that ground-up rhino horns can cure cancer and other ills, the trade has also been embraced by criminal syndicates that normally traffic drugs and guns. They have branched into the underground animal parts business because it is seen as "low risk, high profit," U.S. officials say.

"Get caught smuggling a kilo of cocaine, you will receive a very significant prison sentence," said Ed Grace, a deputy chief with the U.S. Fish and Wildlife Service. But with a kilogram of rhino horn, he added, "you may only get a fine."

The typical rhino horn is about 2 feet long and 10 pounds, much of it formed from the same substance as fingernails. Yet it can fetch nearly $30,000 a pound, more than crack cocaine, and conservationists worry that this "ridiculous price," as one wildlife manager put it, could drive rhinos into extinction.

Gangs are so desperate for new sources of horn that criminals have even smashed into dozens of glass museum cases all across Europe to snatch them from exhibits.

"Astonishment and rage, that’s what we felt," said Paolo Agnelli, a manager at the Florence Museum of Natural History, after three rhino horns were stolen from there last year, including a very rare one from 1824.

U.S. federal agents recently staged a cross-country undercover rhino-horn sting operation, called Operation Crash, "crash" being the term for a herd of rhinos.

Among the 12 people arrested: Wade Steffen, a champion steer wrestler from Texas, who pleaded guilty in May to trafficking dozens of horns that he found through hunters, estate sales and Facebook; and two members of an Irish gang — the same gang suspected of breaking into the museums across Europe.

In an email to an undercover agent, an Irish gangster bragged: "Believe me WE NEVER LOSES A HORN TO CUSTOMS, we have so many contacts and people payed off now we can bring anything we want out of nearly any country into Europe."

Corruption is a huge element, just like in the illegal ivory trade, in which rebel groups, government armies and threadbare hunters have been wiping out tens of thousands of elephants throughout Africa, selling the tusks to sophisticated criminal networks that move them across the globe with the help of corrupt officials.

Here in South Africa, home to the majority of the world’s last surviving 28,000 rhinos or so, the government is throwing in just about everything it has to stop the slaughter — thousands of rangers, the national army, a new spy plane, even drones — but it is losing.

The number of rhinos poached in South Africa has soared in the past five years, from 13 killed in 2007 to more than 630 this year. The prehistoric, battleship-gray animals are often found on their knees, bleeding to death from a gaping stump on their face.

"Ever seen a dead rhino?" said Philip Jonker, who works for a private security firm that has gone into wildlife protection. "It’s worse than going to a funeral."

The only answer, some contend, is to legalize the trade, which would flood the market with rhino horns, lower the price and dissuade rhino poachers from risking their lives — or so the argument goes. Rhino horns regenerate, and the horns can be shaved down every few years and sold off without significantly hurting the animal.

One of most passionate advocates of this legalize-it movement is John Hume, a South African entrepreneur who now owns more than 800 rhinos, with names like Curly, Titan, Hillary and Pinocchio, and has amassed a 2,000-pound mountain of horn worth millions of dollars — if he is ever allowed to sell it.

"Why shouldn’t the person who breeds rhino get a reward?" he asks.

Every time Hume’s ranch hands trim down a few rhinos, they organize an armed escort to take the horns straight to a safe-deposit box in a bank because the same gangs that waylay armored bank trucks are now cruising around South Africa looking for rhino horns.

But many wildlife groups say legalizing the rhino trade would be a disaster.

"The consuming power in my country is growing so rapidly that the supply would never meet the needs," said Jeff He, spokesman for the Chinese branch of the International Fund for Animal Welfare. "And besides, it’ll always be cheaper to poach an animal than raise it."

Kruger National Park, an enormous wildlife refuge in South Africa’s northeast, is where many rhinos are being poached. The park lies on the border of Mozambique, a much poorer country still scarred from years of civil war. Park rangers say Mozambican gunmen are pouring through Kruger’s chain link fences, downing rhino left and right.

Some sophisticated poaching rings use helicopters to spot the animals and veterinarians to dart them with tranquilizers. Others don women’s shoes, to leave misleading tracks.

"At any one time, there are up to 10 groups operating inside the Kruger," said Ken Maggs, a South African National Parks official. "These guys are trying new methods daily."

Scientists say that maybe 1 million rhinos once roamed the earth, and for some reason, humans have been fascinated with the horn for ages. The ancient Persians thought rhino horn vessels could detect poisons. The Chinese thought rhino horn powder could reduce fevers. The Yemenis prized the horn for coming-of-age daggers, presented to teenage boys as a sign of manhood.

In Asia, faith in traditional cures runs strong, fueling demand as Asian economies grow, though there is no scientific proof rhino horn can cure cancer.

In 2008, a Vietnamese diplomat in South Africa’s capital, Pretoria, was caught on camera receiving rhino horn — in the parking lot of the embassy. Around the same time, a Chinese company opened a secretive rhino breeding center in China’s Hainan province, reportedly to produce rhino-based medicine.

In the past 50 years, the overall rhino population has plummeted by more than 90 percent, despite an international ban on the trade in rhino parts since 1977.

But in South Africa, it is legal to hunt rhinos, creating the loophole that the Thai prostitutes sauntered through. Hunters must agree to keep the horn set (rhinos have a large front and smaller back horn) as a trophy and not sell it, and hunters are allowed to kill only one white rhino every 12 months. (Black rhinos are critically endangered and very few are hunted in South Africa.)

According to South African law enforcement officials, gang leaders in Thailand and Laos decided that to maximize the number of rhinos they could kill, they would enlist Thai prostitutes who were already in South Africa with valid passports, which were used for the hunting permits. The women then tagged along on the hunts, often dressed in catchy pinks and blues, but somebody else — usually a professional hunter — pulled the trigger.

"I don’t know whose idea it was to use the ladies, but it was a damn good one," said O’Sullivan, the private investigator.

None of the two dozen or so prostitutes involved have been prosecuted — the intent was to get the big fish. So O’Sullivan leaked a photo of an enormous stockpile of ivory and rhino horns to one of the women, along with a message for her boss, a bespectacled Thai man named Chumlong Lemtongthai, that everything was for sale: "I wanted the big man himself to come here and negotiate."

Lemtongthai did exactly that, and he was arrested soon after. He pleaded guilty and was sentenced in November to 40 years.

"I do not want to see a situation where my grandchildren will only be able to see rhino in a picture," said the judge, Prince Manyathi.

© 2013 The New York Times Company