Blood was spilled on both sides, and there were brawls and vandalism, and when mine owners were killed, coal barons sent in their own private police force — the Pinkerton National Detective Agency — to infiltrate the Irish miners, dubbed the "Molly Maguires" after an Irish woman who led revolts against English landlords. On June 21, 1877, a day known as "Black Thursday," four Irish miners were hanged inside the Carbon County Jail for murder, while six others were hanged in Pottsville.