Allan Pinkerton established his National Detective Agency in 1850, a time when public policing was only beginning to resemble the organized police departments that are common today and well before the federal government played a role in policing. Based on his experiences in public law enforcement, he was able to establish a business that, like the Burns Detective Agency, crossed public and private boundaries in its investigative work for private companies and for the fledgling federal government (Siringo, 2006).
When the Bureau of Investigation, the forerunner of the modern Federal Bureau of Investigation, was formed in 1908 it relied on the investigative methods employed by both the Pinkerton National Detective Agency and the Burns Detective Agency as its model (Morn, 2007). Pinkerton, a native of Scotland, came to the United States in 1842, in part fleeing from arrest in Glasgow for his membership in the Chartists, a revolutionary group that was demanding a greater voice in government for those at the bottom of the economic ladder (Horan, 2007). He settled in Chicago and worked as a barrelmaker, but soon moved to Dundee, a small community 40 miles from Chicago that was heavily populated by Scots. After observing evidence of a number of crimes and reporting this to the Kane County sheriff, he was named a deputy by the sheriff and eventually paid to work on a local counterfeiting case. The successful resolution of the matter is said to have led the Cook County sheriff in 1846 to offer him a fulltime job as an investigator, which resulted in his return to Chicago (Siringo, 2006). By 1848, he had amassed an impressive number of arrests for burglaries and homicides, which led to the U.S. Post Office hiring him in Chicago as a special agent to investigate mail fraud and theft.
Chicago was growing rapidly and crime grew with it. Pinkerton's reputation as a skilled investigator continued to grow when he was employed by the Chicago Police Department, which had not yet formed into the recognizable 24-hour police force that it would become in 1855. Chicago had already become a hub of industry, and officials of a number of companies of one of the leading industries, the railroads, were plagued by theft and vandalism. They approached Pinkerton to form the nucleus of what would become his life's work (Morn, 2007).