MALVERN, Pennsylvania (Reuters) - On a cold winter's day, historian Bill Watson found himself standing in the snow, picking through the roots of an upturned stump near railroad tracks in a place now known as Duffy's Cut.
The exposed roots once held in their grip buttons, human bones and old coffin nails - vital clues in a centuries-old unsolved mystery.
The stump, pulled up several years ago, stood over the final resting place of seven of 57 Irish laborers who perished at the railroad construction site in 1832, during an outbreak of cholera. Also found at the scene was a skull that had been pierced by a bullet and cleaved by a hatchet.
"It's not just cholera," said Watson, who with his twin brother and fellow historian, Frank Watson, is leading the excavation project to piece together what may turn out to be a grisly tale of anti-immigration violence from the 1800s.
For the last 10 years, the Watsons and their research team have struggled to find out what happened to the crew toiling under a boss named Philip Duffy, as they cut a swath through the heavily wooded terrain to lay train tracks about 20 miles northwest of Philadelphia.
The brothers' interest in the site began in 2002, when they discovered references to the immigrant laborers in a document file compiled nearly a century ago by Pennsylvania Railroad president Martin Clement and later kept by his personal assistant - the Watsons' grandfather.
Those documents indicated that all 57 laborers, hired right off the boat from Ireland, died of cholera within six weeks of arrival. The number was far more than the eight deaths listed in local news accounts at the time.
While the cause appeared to be cholera, physical evidence uncovered at the scene also hinted at cruelty and murder, the Watson brothers said.
"We have no idea what percentage of these guys were murdered," said Bill Watson, who chairs the history department at nearby Immaculata University. "But if we have 57, it's the worst mass murder in Pennsylvania history."
Ground-penetrating radar found what researchers believe is the grave site on land now owned by Amtrak. Excavating there could yield vital clues.
But the project has stalled while awaiting permission from the rail company to dig near its tracks. The team has been quietly relying on a network of political backers to press Amtrak for the go-ahead. Negotiations are ongoing, but the historians and the railroad remain hopeful.
"We are optimistic that a plan can be devised allowing safe access to the location for the research team to continue their project while not interfering with railroad operations or compromising anyone's safety," Amtrak said in a statement.
The team began digging in 2004, unearthing tobacco pipe shards and old forks. Those findings alone raised suspicions because, the Watsons said, poor laborers would not have discarded such useful, valuable items.
Then, in 2009, the team found a human tibia, or shin bone.
In all, they found the remains of seven people - all near the old poplar tree - three exhibiting signs of having met a violent end. Exactly who killed them is not known.
The most likely scenario, the historians say, is that the laborers had been isolated because of the cholera outbreak but some of them broke quarantine and local residents, already angry that an influx of Irish laborers had suppressed wages, lashed out in a wave of anti-immigration violence.
Janet Monge, a forensic anthropologist at the University of Pennsylvania who has worked on the project, said the importance of Duffy's Cut goes beyond the story of Irish immigration. It provides vital clues about the lives of early industrial age workers.
"It was a cruel and rugged existence that characterizes the immigrant experience, and it speaks very broadly of the xenophobia that existed at the time," Monge said.
The team has been able to identify one of the bodies as that of John Ruddy, who died at age 18 and whose family members in Ireland share a rare dental feature. Last year, they traveled to Ireland to repatriate his remains.
Over the years, the project faced significant hurdles, including a lack of funding. A nearby cemetery donated a plot for the interment of any other remains found at the site and funds are being raised to pay for a marker. A DNA lab has signed on to test some of the remains.
For Irish immigrant Joe Devoy, a construction contractor who has volunteered at the Duffy's Cut excavation site and worked behind the scenes to push the project forward, the laborers paved the way.
"If they hadn't gone through what they went through, I don't know if my arrival to America would have been a happy one," Devoy said.
Editing by Barbara Goldberg and Gunna Dickson