New searches are under way in the US to try to find the remains of 51 Irish railroad workers who died - or were murdered - in 1832.
Fifty-seven workers were hired to build a stretch of railway in Pennsylvania known as Duffy's Cut.
However, within weeks all of them were dead.
It is thought some died from cholera, while others were murdered by local people who believed the immigrants were spreading the disease.
They all hailed from counties Tyrone, Donegal and Londonderry.
Six sets of remains have previously been uncovered and the new searches that are taking place are at what is believed to be the site of a mass grave containing the remaining 51.
In July, a funeral mass and burial took place at St Patrick's Church in Clonoe, near Coalisland, County Tyrone, for one of the migrants - 29-year-old Catherine Burns.
Injuries to her skull indicated she had been murdered.
The new search site is about 50 yards from where the other remains were found.
Duffy's Cut and its story have been brought to light over the past 12 years by brothers Frank and William Watson, a Lutheran minister and a historian at Immaculata University.
Dr Frank Watson said the site currently being searched is close to the modern railway line.
They had to negotiate with Amtrak, the national railroad in the United States, to carry out the dig.
"What we are conducting now are core samples at the site of what we believe is the mass grave of the remaining 51 labourers at Duffy's Cut," he said.
"We have core samples being taken between 20 and 30 feet along an area underground that our geophysicist indicated looks like the mass burial place.
"If we find human remains in these core samples, our intent is to excavate the remains and re-inter them in the United States and Ireland as we have already done with the first six bodies who were buried at the base of the 1832 railroad tracks."
The new searches are close to a stone memorial wall that was built for the migrants in 1909.
"That wall replaced an earlier 1872 wooden fence put in place by Irish-American railroaders who wanted to remember those who died at Duffy's Cut," Dr Watson said.
"Anti-Irish and anti-Catholic sentiment combined with fear of a worldwide cholera pandemic that hit Chester County, Pennsylvania in the summer of 1832, led to the vigilante violence at Duffy's Cut."