It has been a while since I've mentioned Philip Troutfetter on this blog, comments on another post reminded me of this letter I have from 1900 that discusses the investigation of Troutfetter by the United States Post Office.
W. T. Sullivan's papers are in the possession of the Kansas Historical Society, which is where they were obtained. He was an the inspector in charge of the Denver division of the Office of Post Office Inspector. This letter is dated 6 July 1900 and summarizes his investigation into Philip Troutfetter
The letter is fairly long, but the part of it that addresses the surveillance of the mail received by Troutfetter's sister, Mrs. A. J. Senter (of North Platte, Nebraska), is addressed here:
Sullivan goes on to mention that the Pinkerton Investigative Agency was also investigating Troutfetter. Attempts to locate those records have not brought forth any information.