SHISUN VILLAGE, China — The three miners befriended a lonely, luckless man and offered him work down an iron mine in eastern China.

After working together for 10 days, the three pushed a 220-pound boulder down a steep tunnel, crushing the man to death. They reported it as an accident.

Days later, three men and a woman turned up at the mine, saying they were the dead man’s relatives and demanding compensation. The mine owner offered them $110,000 if they agreed not to report the death to officials.

Prosecutors and the police now say that this death, in Shandong Province in 2014, was one of many in which a sophisticated network of grifters dispatched isolated, hard-up men, some mentally impaired, and dressed up their deaths as accidents to swindle compensation from mine owners.

The investigation led the police to Shisun Village in southwestern China, where mine murders for cash appear to have become a cottage industry. Of the 74 suspects indicted in late May in 17 killings, up to 40 were from Shisun Village, prosecutors said. The police said they were still investigating reports of another 35 possible victims.

But Shisun is not the only place where such cases have cropped up.

A search of court judgments online and news reports of court verdicts turns up dozens of instances across China of gangs killing vagrants and workers in dark, isolated chambers far underground, and using the deaths to defraud mine owners. There have been at least 34 such cases over the past two decades, Caijing Magazine, a prominent business weekly, estimated in June.

The allegations have prompted anguished debate across China about the social and legal failings that led people to make a living by murdering vulnerable strangers, and fanned speculation about whether the crimes were inspired by a bleak cult movie with a similar plot.

Shisun is a hardscrabble, hollowed-out farming village of 5,000 people nestled in the corn-and-bamboo-covered hills of Yunnan Province.

Many villagers work in factories and on building sites in distant provinces, leaving farming and child care to aging parents and grandparents. Those who stay behind often live in crumbling homes of mud and wood.

But on the main street, rows of three-story concrete houses suggest budding prosperity.

Wang Fuxiang owns one of those houses, as well as a restaurant in a nearby city. With his dapper suits and loud, casual wear, the kind seen more often on suburban golfers than on dirt farmers, Mr. Wang, 39, appeared to be among the lucky few who had escaped the hard life.

But it did not go unnoticed that Mr. Wang and several other villagers would abruptly disappear for days, weeks or months, and return flush with cash, which they often squandered on gambling binges, neighbors recalled. Some thought the men might be selling drugs.

“He never told me what he did,” said Mr. Wang’s daughter, Hu Yun, 17. Nor, apparently, did she try to pin him down on the question.

About two years ago, she started to sense that something was amiss. “I began to get the feeling that there was something not right about the way he’d been making money,” she said recently in an interview at her home.

A middle-aged farmer who lived nearby was blunter. Asking that his name not be used for fear of recriminations, he wrote a letter in case he was ever asked about the cases, which said, “There are eight homes in this little village that have been built from human blood.”

The mystery began to unravel two years ago, when the Yunnan police received an anonymous message saying that the man killed in the Shandong iron mine had been working under another man’s identity. (The victim’s real identity, if it has been determined, has not been announced.) Another mine killing late that year in Inner Mongolia, a region of northern China, also left clues pointing to Shisun Village and nearby areas.

Detectives descended on Shisun and began questioning villagers. What they found were organized gangs devoted to serial killing for cash.