Monitoring the Mails in 1900

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:

I don't know how common it was to supply post masters with copies of handwriting for individuals who were being investigated. Apparently the "P.M." (postmaster) at North Platte was not originally furnished with a handwriting sample of Philip Troutfetter when the investigation was started, but the letter seems to indicate that providing such handwriting was a regular practice. But apparently the post office in North Platte, Nebraska, was monitoring her mail even before they had the handwriting based upon comments the investigator mentions in his letter. I'm a little curious about the practice of "mail monitoring" during this time period, but it may be something that simply has to wait.

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.