In the latter half of the 19th century, Schuylkill County, Pennsylvania, was an area rife with violence. Between 1861 and 1875, a series of violent assaults, arsons and murders was blamed on a secret society of Irish immigrants known as the Molly Maguires. The group had originally emerged in north-central Ireland in the 1840s as an offshoot of a long line of rural secret societies including the Whiteboys and Ribbonmen, who responded to miserable working conditions and evictions by tenant landlords with bloody vengeance.

Faced with the prospect of starvation during the Great Potato Famine, more than a million Irish emigrated to America, where a large concentration settled in the anthracite coal region of Pennsylvania in search of work. Irish Catholics were routinely met with discrimination based on both their religion and heritage and often encountered help wanted signs with disclaimers that read, “Irish need not apply.” Accepting the most physically demanding and dangerous mining jobs, the men and their families were forced to live in overcrowded, company-owned housing, buy goods from company-owned shops and visit company-owned doctors. In many cases, workers wound up owing their employers at the end of each month.

When the Civil War broke out and miners were drafted to join what they perceived to be “a rich man’s war,” they began to rebel. “Coffin notices” threatening death, allegedly penned by Molly Maguires, were delivered to mining supervisors and scabs who planned to fill their roles during strikes, and as working conditions worsened in the 1870s, the violence escalated. In all, 24 mine foremen and supervisors were assassinated.

In 1873, Franklin B. Gowen, president of the Reading Railroad, hired the Pinkerton Detective Agency to infiltrate and destroy the Molly Maguires, whose union organizing became an impediment to increasing railroad profits. Using the alias James McKenna, native Irishman James McParlan spent two and a half years living alongside the coal miners, eventually gaining their trust.

Despite the conflict of interest, Gowen served as the chief prosecutor during the subsequent trials. Based almost entirely on McParlan’s testimony, 20 men were sentenced to death—10 of whom were executed on June 21, 1877, also known as Black Thursday. Although the existence of the Molly Maguires as an organized band of outlaws in America is still debated, most historians now agree that the trials and executions were an outrageous perversion of the criminal justice system. In 1979, more than 100 years following his hanging, John Kehoe—the supposed “king” of the Molly Maguires—was granted a full pardon by the state of Pennsylvania.