By Kai Schultz and  Upmanyu Trivedi

THIS image of a goat-headed yogini was found in a London garden after going missing 20 years ago. — PHOTO FROM ARTRECOVERY.COM

FROM a tiny office in southern India, S. Vijay Kumar scans case files on his laptop with the precision of a forensic scientist. To an untrained eye, the width of a bronze Shiva’s nose or the definition of its knuckles are invisible details. To Mr. Kumar, these are clues on a statue that unlock some of history’s biggest art heists.

For more than a decade, Mr. Kumar has devoted himself to a singular cause: recovering smuggled artifacts from the world’s richest collectors. Along with other civilian detectives scattered across time zones, he has roiled an insular art crowd, helping to seize scores of pieces from major museums and auction houses.

With encyclopedic command of the material, Mr. Kumar hunts for distinguishing marks on antiques, matching archival photographs with offerings in glossy Christie’s catalogs. His network assists police squads, busts smugglers, and scrutinizes customs records. They make little money from the work, he said, leaning on volunteers to send tips through social media and conduct “hard-core background searches.”

“I’m quite a character in that I call a spade a spade,” said Mr. Kumar, whose organization, India Pride Project, maintains a database of several thousand artifacts with questionable provenance. “These objects were never intended for a billionaire’s bedroom.”

His sleuthing follows a strong tailwind. Amid tense disagreements over globalization, the right of a nation to its history, and how to atone for colonial sins, art restitutions have surged in recent years. The illicit trade of cultural goods is big business. Upper estimates of the market’s annual value reach nearly $10 billion. That number makes it one of the world’s most significant black markets, though historians note that valuing the only Euphronios krater is a little tricky.

The scope of seizures has also ballooned, encompassing sandstone sculptures plundered under the Khmer Rouge and a mosaic from one of Caligula’s ships. From 2017 to 2020, law enforcement recovered almost ten times more stolen objects worldwide than the number reported missing, according to Interpol’s Works of Art team. Data comes from the organization’s 195 member countries, though not all submit figures.

Powerful institutions have not been spared. Facing prosecution, the Metropolitan Museum of Art surrendered a golden mummy coffin after learning that it was stolen during the Arab Spring. Traffickers dumped the corpse into the Nile before it ended up in New York, where Kim Kardashian posed next to it at the Met Gala. The museum apologized to Egypt and reformed its acquisition policies.

“We rely on disgruntled employees to tell dirty secrets,” said Lynda Albertson, the chief executive of ARCA, a Rome-based organization that studies art thefts and coordinates with the authorities. “And we just stuff them away, like little squirrels putting our nuts in the tree.”

Art crimes are hard to crack. Legitimate sales mix with the shady. Pieces disappear for decades before reappearing on the auction floor. Smugglers fake provenance records and strike during crises. As Russia’s war in Ukraine intensified, conservators hung barbed wire around galleries and hid paintings in basements.

Western nations are increasingly adept at maneuvering around barriers. They have appointed special agents to arrest dealers in five-star hotels, subpoena the e-mails of museum curators, and track terrorist groups using plunder to plot attacks. Money laundering is often a concurrent activity, particularly in financial and trade centers such as Geneva, Dubai, and Malta. In many cases, just a handful of people are responsible for a vast majority of the stolen works in each region.

“There’s been an explosion of interest” in stopping smugglers, said Matthew Bogdanos, who leads the antiquities trafficking unit of the Manhattan District Attorney’s Office, which has returned around 1,700 pieces since opening in 2017. “There’s a lot of really good people out there who have suddenly decided, or realized, ‘Damn, this stuff is irreplaceable.’”

Occasionally, they snag a big fish. Last year, American hedge fund billionaire Michael Steinhardt agreed to surrender $70 million worth of treasure. His collection included a libations vessel that depicts a stag’s head and a Cretan chest used to store human remains.

The biggest hauls often involve India and other Asian nations, where unguarded temples are easy targets. During a bust known as Operation Hidden Idol, officials found goods worth more than $100 million in the New York warehouses of Indian-American art dealer Subhash Kapoor. Mr. Bogdanos said he might stand trial in the US as early as this summer.

Mr. Kumar, 48, knows all about that one. He helped break the case and then wrote a book. The US recently returned 157 smuggled artifacts to Prime Minister Narendra Modi. According to a government report, India recovered less than two dozen pieces in the 35 years before 2012.

“We get random phone calls from unmarked numbers saying they’ve hired a gunman to shoot and all that crap,” Mr. Kumar said. “This doesn’t happen without some bad apples. My stand to them has always been: Sue me.”

A FRAUGHT DEBATELooting is a story of money and conquest.

Genghis Khan called robbing his enemies “the greatest pleasure.” Napoleon’s armies ransacked European cities, snatching paintings from chapels and melting sculptures made of precious metals. In the chaotic weeks after the US invaded Iraq, vandals stole thousands of antiquities from the national museum in Baghdad.

Mr. Bogdanos, a hard-boiled former marine, said that episode was a watershed moment in the world’s awareness about the provenance of artwork. His desk is adorned with dozens of yellow Post-it notes — each one representing an ongoing investigation into purloined works now believed to wrongly be in US hands.

“No one wants to denude museums of their treasure,” he said. “I just want to know that it got there properly. And if it didn’t, it should go back.”

Repatriation pulls support from an unlikely coalition of political groups. In the West, activists on the left frame the debate around righting the wrongs of white supremacy. Factions of India’s religious right argue that Hindu idols are sentient and therefore stealing them is akin to kidnapping.

To date, dozens of nations have ratified a 1970 UNESCO convention against the trafficking of antiquities. But the scars remain: A 2018 report commissioned by the French government found that around 90% of African artifacts are still held outside the continent.

Resistance comes from all quarters. The British Museum has refused to surrender some of its most notable pieces, including the Rosetta Stone. Many private sellers are giving up entirely. A 2019 journal article found that the number of ancient-art storefronts in Manhattan fell from a dozen to three over the previous two decades.

Arguments against returning antiquities span the practical and the philosophical.

Kavita Singh, an art history professor at Jawaharlal Nehru University in Delhi, cautioned against thinking of museums as belonging to a “flat world.” Facilities in poorer countries are often dilapidated. When a million-dollar idol gets publicity, officials cannot simply hand it over to a faraway temple. Many pieces end up in the purgatory of a government storeroom.

For those who subscribe to cosmopolitanism, or the belief in a shared global identity, the location of an artifact is a minor detail. In an age of 18-hour direct flights and hyphenated identities, a Buddha statue holds meaning far beyond Tibet.

“The concern is that these objects should be returned because they are of value to the local populations from which they were taken first, or from which they were purchased,” said James Cuno, the president of the J. Paul Getty Trust, the world’s wealthiest arts institution. “But now those populations are in Berlin. They’re in Delhi. They’re in Beirut.”

HOW TO CATCH A THIEFTo the most devoted art sleuths, academic shades of the debate are ultimately a distraction. A stolen object is a stolen object — and there is nothing like cleaning dirt off a gem.

From his hometown of Chennai, Kumar spoke of Indian art in loving, cinematic detail. His is a lifelong passion. As a young boy, Mr. Kumar’s grandmother instilled in him an appreciation for elegant bronzes from the Chola dynasty.

The path to antiquities hunting took longer. Coaxed by his parents to secure himself financially, Mr. Kumar studied accounting in college and then launched a career as a shipbroker.

But the itch persisted to document India’s rich yet undervalued artistic traditions. Mr. Kumar began visiting remote temples dotted with snake pits. In 2006, he created a blog, Poetry in Stone, likening it to a “dummy’s guide to Indian art.” Through the internet, he found other “heritage hounds,” he said, mostly techies from the subcontinent who scattered during the Dotcom boom. They soon compiled possibly the largest database of missing Indian artifacts.

Within a few years, Mr. Kumar got his big break. He matched items sold by Mr. Kapoor, the New York art dealer, with photographs in French studies of temples from the 1950s. That information was passed to the Indian police and US investigators, who called Mr. Kapoor “one of the most prolific commodities smugglers in the world.”

Since then, Mr. Kumar has helped repatriate pieces from institutions as diverse as the National Gallery of Australia and the Toledo Museum of Art in Ohio. He has also earned a reputation for social media activism. His Twitter is a scrapbook of quotes from obscure art history books. He laments artifacts photographed in the marbled bathrooms of collectors. The hashtag #BringBackOurGods is a constant.

“I have been critical of the law enforcement machinery, the hypocritical art world and the crooks alike, and so I’ve made enemies everywhere,” Mr. Kumar wrote in his book, The Idol Thief, which chronicles the twists and turns of the Kapoor case.

Mr. Kumar insists that pressure is necessary. Traffickers are rarely prosecuted.  Many probes go nowhere. Technology has tilted power from a few ringleaders to a diffuse network of scrappy smugglers who communicate using Google Translate. Badgering police is part of the gig. “If they do their job, we clap,” he said. “If they don’t do their job, we go to the press.”

Collaboration with other art sleuths greases the wheels.

Last fall, Chris Marinello, was standing in a widow’s garden outside London when he made a startling discovery: the long-lost sculpture of a goat-headed deity — all 10,000 pounds of her.

“I was quite moved,” said Mr. Marinello, who was hired by the woman to conduct due diligence on pieces at her country estate.

Mr. Marinello, a lawyer and the founder of Art Recovery International, started to research the sculpture, known as a yogini, a goddess and master of tantra. He contacted Sotheby’s. He consulted a British historian. Then he reached out to Mr. Kumar’s India Pride Project. “Do you know anything about this piece?” he wrote in an e-mail. “This is an important and significant yogini which we have been trying to locate for over two decades,” Mr. Kumar replied.

Mr. Marinello shared high-resolution photos. Mr. Kumar contacted police in the Indian state of Uttar Pradesh. Officials confirmed that several yogini statues were looted from the village of Lokhari around 1980.

The widow, in her 90s, agreed to give up the piece. The men approached the Metropolitan Police, who confirmed that she had acquired the moss-freckled yogini with the house. This year, at a handover ceremony in London, Indian diplomats showered it with flower petals. “The goddess made her way home,” Mr. Kumar said.

CRYING MOMENTSThe euphoria of finding an object lost in time makes up for frustrating dead ends.

Reunions are emotional. The most rewarding restitutions are often anchored in painful histories. Arthur Brand, a Dutch detective, recalled a painting that was seized from Jewish gallerists in Nazi Germany. The Louvre, where it ended up, returned the piece to their granddaughter eight decades later.

“When you see somebody’s face in this particular moment, it’s like a bridge to the past,” he said. “The whole family starts to cry, her new family, because the rest are not there anymore.”

For Mr. Kumar, the stakes are on vivid display in India’s hinterland.

On a recent day, a cluster of barefooted men surrounded him the moment he exited his car in Sivankoodal, a speck of a village fringed with coconut trees. “Have you got the posters?” one asked. Mr. Kumar unfurled several silkscreened banners. They depicted an 800-year-old sculpture looted from the main temple decades ago. The statue portrays the Hindu gods Shiva and Parvati, along with their son. Mr. Kumar said it sits in the Asian Civilizations Museum.

“You tell anyone who asks you about the banner that the idol has been smuggled to Singapore,” he said. The museum didn’t respond to requests for comment.

Mr. Kumar inspected the temple, a low-lying structure festooned with fairy lights and surrounded by mongoose burrows. Inside, he read stone inscriptions dating to Rajendra the Great. “If we get the idol, future generations will benefit,” said Sigamani, 63, a sweat-slicked farmer who goes by one name.

The statues that remain are beating hearts here. A priest clothes them in saris and applies turmeric paste to their foreheads. New idols are submerged in tubs of rice, as if in a womb. After they are removed, believers consider them living entities.

These are galvanizing trips for Mr. Kumar. Reflecting on the number of pieces still missing, anger contorts his words. He rails against museums that display idols in “glass cages,” reducing them to showpiece curiosities. He seems pained when describing traffickers who hack off the arms of statues for transport or sully their complexion with synthetic paint.

His mission has no shades of grey. The chase is addictive, he said, and something like an obsession. But it’s also one Mr. Kumar believes has a vital taproot: conferring dignity at the margins of society. It’s a cause he can’t give up.

“We’re preparing for a long-drawn-out battle,” he said. “We will make sure that a stolen object cannot be sold. We will not let you put price tags on our gods.” — with assistance fromChristian Berthelsen, Bloomberg