McParlan came to national attention when, as an undercover operative using the name James McKenna, he infiltrated an organization of rebellious Pennsylvania coal miners called the Molly Maguires. The Molly Maguires originated in Ireland in the 1840s as a secret society dedicated to fighting the mounting agricultural oppressions in their country. In the early 1860s with the outbreak of the Civil War, a loosely organized, mostly reactive version of the Irish Molly Maguires allegedly emerged in the coal region of Pennsylvania where many Irish immigrants had settled. Between 1862 and 1868, the Molly Maguires are said to have assassinated six mining officials and supervisors with whom they or their secret society fellows had employment grievances. The Molly Maguires were credited with eight more assassinations between 1874 and 1875. The alleged Molly Maguires were arrested, brought to trial, and convicted on the testimony of a Pinkerton detective, James McParlan, who had been hired by Gowen. Twenty men were sentenced to death; ten of whom were hanged on the same day, known as Black Thursday, June 21, 1877. Molly Maguire history is sometimes presented as the prosecution of an underground movement that was motivated by personal vendettas, and sometimes as a struggle between organized labor and powerful industrial forces. Illustration originally captioned: McParlan (on knees) initiated as a Molly in "Muff" Lawler's bedroom, 1874.