Before his research team's latest discovery, historian William Watson only suspected that something sinister had happened in Chester County when a group of Irish railroad workers died mysteriously in 1832.

Now, the Immaculata University professor is more certain: It probably involved murder.

At least six of the 57 men who traveled from Ireland to work on the Philadelphia & Columbia Railroad were likely killed in the midst of a cholera epidemic, researchers say.

"They were expendable because they were Irish Catholic immigrants at the bottom of the economic ladder," Watson said this week. "No one was there to advocate for them."

Their bones tell the story. Four skulls unearthed from the East Whiteland Township site believed to be the workers' encampment show signs of blunt trauma, researchers say. One unearthed this month has a hole that might be from a bullet.

The probability of murder is the latest finding in the Duffy's Cut Project, a nearly 10-year effort spearheaded by Watson and a team including his twin, the Rev. Frank Watson, also an historian.

Researchers are investigating the fate of 57 Irish immigrants who sailed from Donegal, Tyrone, and Derry Counties for Chester County in June 1832.

The men lived in a shanty and worked on a section of nearby railroad tracks known as Duffy's Cut. They faced anti-Irish sentiment, the cholera epidemic, and quarantine. By the end of August, they were dead.

Their deaths had been the subject of speculation and folklore until the Watsons and their research colleagues began piecing together a probable scenario from books, diaries, newspaper articles, railroad documents, and human bones.

Most of the men died of cholera, researchers say, but at least six probably met a different fate.

An archaeological dig at the shanty location near Sugartown and King Roads has uncovered what researchers believe are the graves of seven of the men. In them, they found the bones of six and the skulls of four.

Most of the artifacts were found last year, but two of the skulls were unearthed on Aug. 4 and 5.

With two additional skulls also showing signs of trauma, the case for murder became more concrete, said anthropologist Janet Monge, a member of the research team and the keeper of skeletal collections at the University of Pennsylvania Museum of Archaeology and Anthropology.

One of the skulls discovered this month with a hole in it also has a gash on a side that could have been made by an ax, Monge said.

"When you start to see many dramatic events in many different skeletons in and around the time of death, then you start to think that it's not accidental," Monge said.

The Watson brothers first suspected something ominous when they read about the workers in files that they inherited from their grandfather Joseph F. Tripician. Tripician, of Narberth, was the private secretary to Martin W. Clement, who served as president of the Philadelphia & Columbia for 16 years starting in 1933.

Documents show that all 57 workers had died of cholera. The brothers were suspicious. Watson said, as the disease's mortality indicates that only 40 to 60 percent of that group should have died.

Information in the file also led them to the burial site.

They enlisted the aid of Monge, the County Coroner's Office, geophysicist Timothy Bechtel, and Earl Schandelmeier, an adjunct professor at Immaculata, as well as student assistants Robert Frank and Pat Barry. Another member of the group, Immaculata professor John Ahtes 3d, died last month.

William Watson said he believes the immigrant workers fell victim to prejudice and xenophobia during a time when people feared the spread of cholera so much that newspaper accounts describe families' shunning infected relatives and leaving them to die alone.

Researchers say they believe a mass grave containing the remaining workers is in a ravine just west of the location where the remains were unearthed.