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
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.