On June 21, 1877, a day that will long be remembered as Black Thursday, ten members of the Molly Maguires, an Irish labor organization, are executed in Pennsylvania, the first of twenty executions that make up the largest mass execution of any group by the U.S. federal government in history.

The Molly Maguires is an Irish 19th-century secret society active in Ireland, Liverpool, and parts of the eastern United States, best known for their activism among Irish American and Irish immigrant coal miners in Pennsylvania. The Mollies are believed to have been present in the anthracite coal fields of Pennsylvania in the United States since at least the Panic of 1873.

Members of the Mollies are accused of murder, arson, kidnapping and other crimes, in part based on allegations by Franklin B. Gowen and the testimony of a Pinkerton detective, James McParland, a native of County Armagh. Fellow prisoners testified against the defendants, who were arrested by the Coal and Iron Police. Gowen acts as a prosecutor in some of the trials. The Molly Maguires become largely inactive following the executions of 1877 and 1878.

On June 21, 1877, the first ten executions take place. Six Mollies – James Carroll, James Roarity, Hugh McGehan, James Boyle, Thomas Munley, and Thomas Duffy – are hanged in the prison at Pottsville, Pennsylvania. The sheriff hangs them successively two-by-two rather than build special gallows to accommodate six. An immense crowd gathers covering the surrounding hills. Boyle carries a blood-red rose and McGehan has two roses in his lapel. Carrol and Roarity declare their innocence from the scaffold. In County Donegal, McGehan’s relatives meet in the kitchen and, it is said, the sky blackens at the moment of hanging.

On the same date, Alexander Campbell, John “Yellow Jack” Donohue, Michael J. Doyle, and Edward J. Kelly are hanged at a Carbon County prison in Mauch Chunk for the murders of John P. Jones and Morgan Powell, both mine bosses. Here gallows have been erected to accommodate four hangings and the four are hung at the same instant. Campbell, just before his execution, allegedly slaps a muddy handprint on his cell wall stating, “There is proof of my words. That mark of mine will never be wiped out. It will remain forever to shame the county for hanging an innocent man.” The handprint remains to this day.

Ten more condemned, Thomas Fisher, John “Black Jack” Kehoe, Patrick Hester, Peter McHugh, Patrick Tully, Peter McManus, Dennis Donnelly, Martin Bergan, James McDonnell, and Charles Sharpe, are hanged at Mauch Chunk, Pottsville, Bloomsburg, and Sunbury over the next year. Peter McManus is the last Molly Maguire to be tried and convicted for murder at the Northumberland County Courthouse in 1878.