The Irish immigrants building a stretch of railroad near Philadelphia in 1832 had been in the U.S. only a few weeks when they died _ ostensibly of cholera _ and were unceremoniously dumped in a mass grave. Their families never knew what happened to them.

Nearly 180 years later, local researchers say they have a clearer picture of the men's fate. But their massive effort to unearth, identify and properly re-inter the workers' remains will not be realized; the grave is inaccessible, they say, and will remain undisturbed.

Still, enough evidence exists to prove that some laborers were victims of murder, not disease, according to historians Frank and Bill Watson. And while it's likely the unrecovered bones may have been too degraded to yield testable DNA, one set of remains found apart from the main ossuary might still be positively identified and returned to Ireland.

"Since the beginning, we have seen it as our job to get their story out of folklore and into actual history, and we hope we have done that," Bill Watson said.

The brothers' years-long quest, known as The Duffy's Cut Project, began nearly a decade ago and aimed to reveal the true fate of 57 workers from Donegal, Tyrone and Derry who helped build the Philadelphia and Columbia Railroad.

A stone monument along active tracks in East Whiteland Township says the immigrants died of "black diphtheria" in 1834. But papers belonging to the Watsons' late grandfather _ who worked for the railroad long after the Irishmen died _ indicated the men had perished two years earlier.

The supposed cause was cholera, a contagious and then-common intestinal disease. But cholera in those days had a mortality rate of 40 to 60 percent, so not all of the immigrants succumbed. How did the other men die?

The Watsons, who both hold doctorates in history, theorized that while cholera killed many of the laborers, the rest were likely victims of local vigilantes driven by anti-Irish prejudice, class warfare or intense fear of the dreaded disease.

And then they went out to prove it.

Because the 49-year-old twins have no formal archaeological training, they worked with volunteer experts in fields including forensics, anthropology and geophysics. Immaculata University, where Bill Watson heads the history department, has provided some funding.

The laborers had begun working for Philip Duffy on a section of track about 20 miles west of Philadelphia in June 1832. By August, they were dead.

More than a century later, the Watsons' team began combing a small, woodsy valley behind a manicured subdivision only to find household artifacts like pipes, buttons and forks _ likely from the immigrants' shantytown.

Quite a few residents thought the brothers were chasing ghosts, said East Whiteland Township Manager Terry Woodman.

"Some people thought that this was lore, a story that through the telling had been exaggerated," Woodman said. "There was a lot of skepticism."

Then in March 2009, the Watsons found a shin bone.

Over the next two years, their group would unearth six sets of skeletal remains, along with evidence of a seventh set that had decomposed. The brothers surmise these men _ and one woman _ became sick and tried to leave the camp, only to be killed by vigilantes.

University of Pennsylvania anthropologist Janet Monge found proof of violence in all the remains, including one skull injury that appears to be a bullet wound.

Those victims had been buried separately in coffins. But after the rest died _ from disease or violence _ Philip Duffy ordered the bodies dumped en masse in the railroad fill, according to the brothers' research. The shantytown was burned.

The location of the mass grave remained elusive until recent weeks. A radar survey of the land beneath the stone monument a few years ago yielded nothing, so the Watsons assumed the marker was inaccurate.

But geophysicist Tim Bechtel recently used more sophisticated techniques, including electrical imaging and seismic surveys, to conclude the ossuary is likely near the monument after all _ but 30 feet below the surface.

It's also on Amtrak property. The rail company will not permit any digging because of its proximity to the tracks, spokeswoman Danelle Hunter said.

"I don't blame them for not being keen on excavating there," Bechtel said, noting the difficulty of shoring up the rails during such an extensive dig.

That decision has ended the brothers' field work, their plan to reclaim all of the immigrants' remains and, through DNA tests and other analysis, fully identify and re-inter them properly.

While disappointed, Frank Watson said the most important point is that history will not remain buried with the men.

"We have put flesh to the bones of the story of their lives and deaths," he said, "and their sacrifice to help build a small corner of the modern world will no longer be forgotten or hidden."

Even if the bones were accessible, it's likely they would be too degraded to extract DNA. Monge, the anthropologist, said that was the case for most of the recovered remains, although tests pending on a few teeth might yet yield some information.

The brothers had tentatively identified one victim as 18-year-old John Ruddy, based on bone size and the passenger list of a ship that sailed from Ireland to Philadelphia four months before the men died.

That victim's jaw also had a rare genetic anomaly _ a missing upper molar that never formed _ shared by some Ruddy family members in Ireland. If the DNA matches, the Watsons hope to bring Ruddy's remains back to Donegal.

The brothers plan to bury the rest of the remains in a suburban Philadelphia cemetery around St. Patrick's Day, March 17.

Dennis Downey, a history professor at Millersville University, said the team's research offers valuable insight into 19th-century U.S. attitudes toward immigrants, industrial work, disease and culture.

"You see industrial history, you see immigration history, you see the broad contours of changing cultural history," said Downey, who is also an officer in the Lancaster (Pa.) Irish American Cultural Society, which has supported the project.

Michael Collins, Ireland's ambassador to the U.S., has visited the Duffy's Cut site twice. In a statement to The Associated Press, Collins said he was struck by the tale of immigrants "arriving here full of optimism and hope only to die so anonymously and tragically."

"Their story needs to be told," Collins said. "So many from Ireland helped to build America but it was not an easy life, or an easy time."

Indeed, the Watsons say what happened at Duffy's Cut was not an isolated case.

Their next investigation involves another possible mass grave of Irish railroad workers about 10 miles up the tracks in Downingtown. Two other sites suggested by local historians could follow.

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Online:

http://www.duffyscutproject.com

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Kathy Matheson can be reached at http://www.twitter.com/kmatheson.