This paper evaluates the role of private policing in the patterns of violence that were prevalent in the mining regions of eastern Pennsylvania during the 1860s and 1870s, and which were attributed to an Irish secret society called the “Molly Maguires”. This topic has long been subject to academic and political controversy, and the use of agent provocateur tactics by the Pinkerton agency has been strongly suggested, but never conclusively proven. Drawing on existing research on secret societies, private policing, and the role of the agent provocateur, this paper combines two strands of research that have so far largely been discussed separately. The study then attempts to close the gap on the agent provocateur question by applying methods from criminological history. Through treating different sources as conflicting testimonies, as well as using GIS to provide new insights on crime patterns in the region, it analyzes the complex relationship between undercover policing and the groups under its surveillance. The results provide decisive new evidence regarding the agent provocateur question and the role of the Pinkerton agency during the Molly Maguire trials, as well as the character of the surviving evidence.