Allan Pinkerton was an exceptional individual; his biography is quite entertaining and filled with adventures. I recommend anyone interested to read the article; Roots of a Detective at the Crime Library website.
Pinkerton was born on August 25, 1819 in Scotland. He was a cooper (barrel maker) by trade and left Scotland in 1846 with his new bride, Joan Carfrae. After a rough voyage, Pinkerton and his wife managed to reach Chicago where he started to work for a barrel manufacturer. One thing lead to another and soon Pinkerton changed his profession and established the "Pinkerton National Detective Agency" in 1850. It began as a security guard agency, but through the 19th century the agency would become both a private military contractor and security for many businesses needing strikebreaking measures. In 1871 the Department of Justice contracted the Pinkerton agency to detect and prosecute those guilty of violating federal law.
From a genealogical and historical perspective, the Pinkerton agency was involved in many major historical events such as foiling a plot to assassinate President Abraham Lincoln; infiltrating the Molly Maguires; helping squash the Homestead Strike; and tracking down famous western outlaws like Jesse James, the Reno brothers, the Wild Bunch, and Butch Cassidy and the Sundance Kid. At one time the Pinkerton Agency had a standing army larger than the United States army. The state of Ohio even went so far as to outlaw the agency due to fears it would be hired as a "private army."
Can you imagine what kind of historical accounts are among the case files of the Pinkerton agency! In the year 2000, the agency gave over 150 years of files to the Smithsonian Institute in Washington, D.C.. The collection spans from 1853 to 1999 with the bulk of the dates between 1880 and 1920. The collection has 63,000 items in 183 containers which equals to 79 linear feet. The collection is presently in the Manuscript Division of the Library of Congress in Washington, D.C.. Unfortunately, the collection is limited to the Chicago, New York, and Philadelphia offices. Many of the records from smaller branch offices in the West did not survive. The collection is described in a finding aid that is posted on the Division's website at http://www.loc.gov/rr/mss/f-aids/mssfa.html.
Among the highlighted items are photographs, drawings and documents on Jesse James, the Hole-in-the-Wall Gang, the Missouri Kid and Butch Cassidy. You can look at the index of the containers on line at: http://www.loc.gov/rr/mss/text/pinkerton.html.
Unfortunately, the index is only a starting point. I have not found the contents of each of the 183 containers to be accessible by computer. I queried the librarian at the Library of Congress at email@example.com concerning how one could access the genealogical data. It turns out boxes 27 to 34 are the "Administrative Files" which contain employee files. Although James Green was not listed as an employee, the librarian did find in box 39 that a Green was an operative. The collection is cross referenced with the book; A Detective Dynasty by Richard Wilmer Rowan, published by Boston: Little Brown Company in1931. In this book it mentions that a James Green was an associate of the George Wade Wilkes gang. The Wilkes gang was into forgery in New York city. It is unsure that my James Green whom is buried in Raton, New Mexico, is the same mentioned in the above references.
One can research the records of the Pinkerton agency in the Manuscript Reading room or a librarian can mail you a list of private researchers who can search the records on your behalf. This is another rich source of both American and family history. There are first eye-witness accounts of colorful characters which can not be found any other place.