THA BAK, Laos — He was up there somewhere, at the top of the hill, the man Karl Ammann had come to see. It would soon be night. The forest was all shadows and sounds. Ammann had driven across the country to reach this remote river village, and now he was finally here, looking to the top of the hill, ready to confront the person he believed had murdered more tigers than anyone in Laos. In the distance, he could hear them: dozens of tigers roaring.

For nearly five years, Ammann, 70, a Swiss counter-trafficking conservationist, had tracked the tiger butcher, a man named Nikhom Keovised. He had placed hidden cameras inside what had once been the largest tiger farm in Southeast Asia, an illegal operation where tigers had been raised to one end — slaughter — and where the man doing the slaughtering had been Nikhom. And he had listened to Nikhom describe it all in his own words: “Use the anesthetic,” he had said. “Then just cut the neck.” Then “peel its skin.”

Now Nikhom had established himself here, in this half-splash of civilization near the Vietnam border, where he’d just opened what his boss — considered one of the nation’s biggest wildlife traffickers — described as a zoo, but what Ammann suspected was a front for selling tigers.

Ammann knew the risks. He was in the country without permission to investigate its wildlife practices. He was unarmed. Neither Nikhom nor his boss, who didn’t respond to repeated requests for comment, had ever been charged with anything, let alone arrested. If discovered, the equipment Ammann had with him — the drone, the hidden cameras, the satellite images of the country’s tiger farms — would immediately unravel his cover story, that he was a tourist here on a lark.

But he could already feel the familiar intensity. It had driven him to undertake dozens of risky, self-funded investigations, pushed him to the fringes of the conservation community and caused even friends to describe him as obsessive, if not a little crazy. He couldn’t stop. Those responsible had to be held to account. Species by species, the world is rapidly undergoing an ecological transformation, becoming barely recognizable from the planet it was a few centuries ago. It is a world reckoning with an end of wildness, where humanity and domesticated animals account for almost all mammal biomass, and the tiger, whose captive population now dwarfs its numbers in the wild, is on the verge of becoming a fully industrialized commodity.

For 10 days late last year, I joined Ammann on an undercover journey to the core of the modern tiger economy to determine whether Laos, a global hub of wildlife trafficking, had fulfilled its promises since 2016 to stamp out the wildlife trade. The trip had been dangerous from the beginning, and then gotten riskier, and now we’d arrived to this hill, where, above, the tigers were becoming louder.

They were hungry, Ammann announced. It would soon be time to feed them. He slung his camera over his shoulder and started up the hill, in search of tigers and their warden.

Over the past century or so, the tiger population has plunged in the wild, dropping from an estimated 100,000 to fewer than 4,000, while the number in captivity has exploded to more than 12,500. Nowhere else is the animal’s commodification more complete than in tiger farming, where it is raised, butchered for parts and sold for tens of thousands of dollars. And nowhere else have these farms operated with greater impunity than in Laos, an obscure communist nation whose own wild tigers have nearly all been killed. Ammann was one of the few people who’d seen inside the country’s farms.

When I’d first spoken to him in June of last year, I’d expected to find someone who was, if not optimistic, then at least hopeful. In a smattering of countries in South Asia, the tiger’s population appeared to be stabilizing, even as it cratered elsewhere. And since 2016, international authorities and some conservationists had applauded Laos, home to some of Asia’s biggest wildlife traffickers, as it announced overhauls to finally clean up the trade. Shops trading in bones and wildlife merchandise were to cease. All three of the country’s illegal tiger farms, which stored 700 tigers, were ordered to stop farming and convert into zoos and conservation centers. No new facilities breeding endangered wildlife for commercial purposes would open. From the outside, things seemed to be getting a bit better. Even Britain’s Prince William had reportedly taken up the cause.

But Ammann was neither optimistic nor hopeful, and, if anything, seemed offended by the suggestion. In our first substantive phone conversation, he immediately plunged into the arcana of tiger farming in Laos, citing operational tiger farms and going on and on about “lip service” and how we were being taken for “bloody fools.” While Ammann vented, I searched for images of him. He looked the same in every one: mustachioed and grimacing, an expression of the frustration and futility in his voice.

“They all want hope and happy endings,” he said of producers and audiences who ignored his documentaries, despite their findings. “And I don’t see any happy endings. I can’t create fiction from what I see as fact.”

We ended the phone call, with him promising to send me some photographs and documents from a trip he’d just taken to Laos to work on a documentary about tiger trafficking. I felt dazed. Who was that guy? And if he didn’t feel there was any hope, why did he assume so much risk going into some of the world’s most remote forests, without institutional support or funding, to document the destruction?

From then on, in interviews with conservationists about tiger trafficking, I saved a few questions for the end: Just what do you think of Ammann? Almost everyone I asked immediately knew who Ammann was and said his findings were sound. He could be trusted — but.

But what?

“He takes a lot of risks,” Steve Galster, a counter-trafficking expert in Bangkok, said after a long pause.

“A difficult character,” said Crawford Allan, a senior director at World Wildlife Fund, an international conservation organization with an office in Washington. Ammann had been kicked out of an international conservation meeting for aggressively confronting officials and was known to send environmentalists notes denigrating their work after they’d just trumpeted it in press releases.

“A bit of a kook who gets results,” a law enforcement consultant in Laos, who spoke on the condition of anonymity, called him.

Ammann had sent me some of those results. I pulled up the documents and photographs on my computer, and immediately recoiled.

The first one was of a diseased tiger in a claustrophobic cage — mangy, eyes desperate, death coming.

The next showed seven tigers eating bloody, raw chicken off the ground, clustered in a line of cramped cages.

Two more were from high above, where Ammann had flown a drone to capture images of two massive tiger farms, showing the animals in cage after cage. He included a 3,700-word missive he’d dispatched to the U.N. commission charged with regulating the wildlife trade, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), accusing the organization of being “a big part of the problem.” He’d sent the same letter to a European Parliament official, attaching this comment: “So you cannot say you did not know. My motto for doing this.”

I called Ammann, who was home in his estate at the base of Mount Kenya, where he keeps as “dependents” two orphaned chimpanzees. I asked whether he was planning on going to Laos again. He said he was — and it would be before year’s end. In the coming weeks, in fact, he’d have the itinerary all planned out. This time, he hoped to take his investigation even further, stepping out from behind the hidden cameras to personally meet those who’d profited from the death of the tiger.

“Why don’t you come,” he asked, “and see for yourself?”

After a 24-hour flight, I arrived at my hotel in northern Thailand past midnight. There was a note waiting for me from Ammann. We’d planned to meet the next morning at 8, given my late arrival, but now the note said that wasn’t early enough. We had to meet at 7. A long day was ahead, and there was no time to waste.

After a fast handshake and a few quick words in the morning, we were inside a van, bumping toward the Laos border. My editors and I had decided that I would enter the country without identifying myself as a journalist, an exception to The Washington Post’s usual practice. I would travel with Ammann and planned to accompany him everywhere, taking notes and quietly snapping photos. If someone asked about my profession or my employer, I knew I’d have to answer truthfully. But no one did.

Ammann wanted to cross into the country by nightfall, where he said the real journey would begin. Landlocked and mountainous, Laos has nearly 1,600 miles of borders with Vietnam and China, whose appetite for illicit wildlife products had both decimated numerous species and transformed Laos into a global epicenter of wildlife trade. Last October, the U.S. State Department again listed Laos as one of three countries whose government “actively engaged in or knowingly profited” from trafficking endangered species. CITES in a 2017 report was even blunter: “Everyone can buy everything and cross the border.”

Over the next 10 days, Ammann planned to traverse much of the country, beginning in a northern region called the Golden Triangle to visit a casino town notorious for wildlife trafficking and investigate rumors of a never-before-identified tiger enclosure. And then he’d head south, stopping to buy tiger products from merchants in the country’s biggest cities, fly drones over tiger farms and search for clues involving the mysterious disappearance of 300 tigers from one of them. Lastly, he’d venture to a new resort and “zoo” named Say Namthurn, where Ammann hoped to finally meet Nikhom, the tiger butcher, along with his boss, Sakhone Keosouvanh, who helped bring tiger farming to Laos.

Inside the van now, along with Ammann, were his cameraman, Phil Hattingh, a towering South African; and a young Chinese woman named Grace Chan. Ammann had met Chan, who’s from Hong Kong, in autumn 2017, after she’d contacted him to discuss elephant trafficking. She’d told him she wanted to save animals, so he had introduced her to what he believed was the best way of doing that — his way.

“They’ll think you’re a customer,” Ammann said to Chan, explaining his plan for her on this trip. “I have the perfect cover story for you.” She was to visit shops all over Laos while wearing a hidden camera to buy tiger products, masquerading as a young assistant to a Hong Kong businessman who wanted tiger parts to impress his friends. To bolster her expertise on the tiger economy, Ammann would soon pull out a tattered book and hand it to her.

It was a taxonomy of tiger bones, showing pictures of the skull, femur, tibia, hip. The book described the bones as a “precious crude medicine,” whose medicinal use in China traced back more than 1,400 years. But as China’s economy grew, the animal’s mythical qualities — none of which are substantiated by modern medicine — ignited a market for tiger products that, the book said, “sold well domestically and abroad.”

So well, in fact, that within years of the book’s 1979 publication, a country as vast as China estimated it had only a few dozen tigers left, and something needed to be done. The Chinese government passed a law that banned killing endangered species in the wild while encouraging their “domestication” and breeding. The idea was that the farms would expand the tiger population, sating demand for tiger products while protecting those in the wild. But that wasn’t what happened. Instead, demand exploded further, said Vanda Felbab-Brown, a Brookings Institution senior fellow who’s studied the industry, inciting rampant poaching of wild tigers all over Asia and ushering in an era of “catastrophic consumption.”

There were efforts to get things under control. Chinese officials in 1993 prohibited domestic trade in tiger bone but didn’t close the country’s many farms, which by 2007 warehoused more than 5,000 tigers. That year, CITES, an international authority with few enforcement tools, banned tiger farming for commercial purposes. China chafed against the restrictions then, and now. Last autumn, it legalized trade in tiger parts for medicinal purposes but, under international pressure, quickly reinstated its ban.

To bypass it, some Chinese customers flock to border towns sprinkled throughout the Golden Triangle area, where the countries of Myanmar, Laos and Thailand converge, and where weaker rule of law and government corruption abet black market wildlife trade. That was exactly what Ammann wanted to investigate first.

We drove into the night, passing miles of undeveloped countryside, until a city sprang out of the blackness like a vision. Lexuses and Mercedes wheeled down its streets with license plates from all over China. Big hotels blinked with green and red lights. People swarmed around a large casino with a crown of gold at the town’s center.

Known as the Golden Triangle Special Economic Zone, this sliver of Bokeo Province is controlled by a transnational criminal operation that “engages in an array of horrendous illicit activities,” including child prostitution and human, drug and wildlife trafficking, according to the U.S. Treasury Department, which last year imposed sanctions on the network. “Sin city,” the London-based Environmental Investigation Agency, a non-governmental organization, called the zone in a 2015 report — a “lawless playground” where an exclusive clientele of Chinese tourists could buy tiger parts in shops and eat tiger meat at restaurants. Just about the only Lao element of the town was geography. Clocks here were set to Beijing time, business was done in renminbi, and the dominant language was Mandarin.

On our first morning here, I could tell Ammann was already exasperated. His driver was not going fast enough, no matter how many times Ammann told him to pick it up. His computer had stopped working. The hotel where we’d spent the night before — the only one that still took Western guests following the U.S. sanctions — had just told us to clear out. And now Chan was running late.

“Come on, Grace,” he said, waiting outside the hotel for her.

“Come on, Grace,” he said, less than a minute later.

“We’ve got to go,” he said again.

“Tell her to come,” he finally snapped, directing his Lao guide to go get her.

Chan finally got into the van, and Ammann told the driver to get moving.

He knew how he sometimes sounded, but there was no time for niceties, not while the world was committing suicide. In conversations, he frequently brought up environmental studies he’d just read, all of them apparently grim. Between 1970 and 2014, vertebrate populations dropped in size an average of 60 percent. One million plant and animal species now face extinction. The planet could soon lose 60 percent of primate species, according to a study in the peer-reviewed journal, Science Advances, noting how bush-meat hunting had sped their demise — a revelation that, to Ammann, wasn’t a revelation at all. It was his origin story.

In 1988, Ammann was in a long boat chugging up the Congo River in what was then Zaire. By then, he’d already spent two decades in Africa, where he had worked as a hotelier and photographer, eventually becoming wealthy opening and selling an eco-tourism camp in Kenya’s Maasai Mara National Reserve. But along the river’s banks, he saw an Africa he didn’t know. Hundreds of slaughtered primates were strewn near the water’s edge, awaiting transport to nearby markets to be sold as bush meat. Deforestation had provided hunters with access to animals previously protected by dense jungle, giving rise to an underground economy.

The bush-meat hunts, the markets, the outrage he’d felt at their discovery: It soon consumed him. In the early 1990s, at a time when little was known about the bush-meat trade, he went to remote merchants and logging encampments, looking for apes orphaned by bush-meat hunters, and returned with gruesome images that few could stomach. Decapitated gorillas. Charbroiled monkeys. Butchered chimpanzees. His photography blurred into activism. He published books, lobbied governments, led international petitions against wildlife slaughter and took nearly every media opportunity that came his way. He described it all as graphically as he could, hoping to shock people into action. “Up to their elbows in blood,” he said of bush-meat hunters in one 1995 newspaper interview. It was “98.5 cannibalism” to eat chimps, he said in another. “Maybe I’ve become too extreme,” he confessed in one more, and many conservationists then agreed.

Jane Goodall, the renowned chimpanzee conservationist, said he was too aggressive, and he said she wasn’t aggressive enough. Other conservationists accused him of “cultural imperialism,” and he countered that they worried more about fundraising than truth.

“He won’t stop,” says his wife, Kathy, even after his findings were substantiated, and he was named a Time magazine Hero of the Environment in 2007 for “almost single-handedly raising awareness of the issue of bush meat,” and was told again and again to slow down. His marriage was suffering. Commitment had collided with obsession. “Just part of the furniture” was how Kathy said she’d come to feel, seeing him at the computer, emailing and researching all day. Two personalities jostle inside him, said Dale Peterson, a former collaborator. He was one person around people — combative, cynical, “miserable,” as Peterson put it — and another around animals. That was the Ammann who’d for decades cared for a chimpanzee he’d saved from hunters, or who would stop and discuss even a small bird, he said, “in the most affectionate way.” He was “driven by something larger.”

That intensity building within, he pulled up to the market along the Mekong River, straddling the Lao-Thai border. The door opened, out Chan went, and from the market entrance, Ammann watched her disappear into the stalls.

She was dressed in black. Black hat. Black sunglasses. Black blouse, the top button of which concealed the camera. Ammann wanted us to keep our distance from her at first, knowing the illegal wildlife trade had increasingly receded from public view, just as it once had with bush meat. Sellers these days store their jewelry and medicine in backrooms and hidden drawers that open only for wealthy Chinese customers — which was how Ammann hoped Chan would appear. He followed her into the market.

Ammann asked to see more. The man pulled out his phone and sent a contact request on the messaging app WeChat to Chan, who held up the screen for Ammann and myself to see.

She already knew the digital netherworld of wildlife trading, where all she needed to do was enter a few keywords — “jelly” for ivory, “king” for tiger products — to thwart a blanket prohibition on the trade on China’s leading commerce sites. The ban, instituted in 2012, had gotten rid of a lot of the listings, but it hadn’t gotten rid of them all, not with an evolving lexicon of code words and not with social media, where much of the trade has migrated and is more difficult to detect. Elephant-skin powder pills, black-bear gallbladder bile and tiger-bone jewelry: Chan had seen it all. But one rare product didn’t appear on the seller’s WeChat profile. Did he have any tiger skin for sale?

“No tiger skins anymore. You can find them in Vietnam,” he said in Chinese. “In Vietnam, there are more tiger farms.”

“But Laos has a lot of tiger farms, too,” Ammann said.

“Tigers in Laos are now protected,” the merchant said.

Ammann looked at him strangely. He knew Laos had vowed to close its tiger farms and stop the trade in wildlife products, but yet here this merchant was, doing just that. So how likely was it that much had changed? The government, after all, had more than two years ago promised a “full audit,” funded by the U.S. Fish and Wildlife Service, to determine the number and origin of the country’s captive tigers. But it had faced numerous delays. And the same tiger breeders the government had previously accused of breaking the law were still involved in the operations, where the tiger population has been fluctuating dramatically, indicating possible trade.

The number of tigers on one farm named Vannaseng surged from 102 to 235, then fell to 111, according to public records and Lao government documents that I reviewed. Another one called Vinasakhone — where Nikhom had worked — reported a sudden loss of 300 tigers in 2017, shedding three-fourths of its population, without ever explaining how that happened. Then a new and massive farm was disclosed by a Vietnamese news outlet in April 2017 in the central Laos town of Lak Sao and as of last year housed 106 tigers. Lao government officials did not respond to repeated requests for comment to discuss these issues.

Ammann, walking away from the stall and the market, believed there were even more tiger enclosures now in Laos, which hadn’t yet been identified. One was rumored to be right here in the Golden Triangle: He had to find out whether it was true.

We drove several miles, coming to a stop on a desolate dirt road wedged between thatched-roof huts and jungle. Ammann got out of the car. This was where an informant had told him to look. Up ahead, he saw a complex of structures behind a tall wall. “Turn the car around,” Ammann said curtly to the driver. “And turn the engine off.” He reached for his camera and approached the walls, from which hung several signs, praising the facility’s supposed role in conservation.

“Caring rare animals, protect the blue planet,” said one in English.

“Growing with animals and die without them,” said another, also in English.

Ammann turned on his camera and held it at his hip.