Are You Checking Manuscript Collections?
Another overlooked source are manuscript collections, materials that may be housed in a library or a private archives, with letters, files and other documents that may have been donated at some point in time.
A google search was how I located information on Philip Troutfetter in a manuscript collection at the Kansas Historical Society. I was fortunate that the finding aid to this Bristow collection was online. If it had not been I would have been unable to locate the reference as easily as I did. I'm working on locating additional papers regarding the investigation into Troutfetter.
Searching World Cat (http://www.worldcat.org) may also bring up some manuscript collection,but bear in mind that only the "main" names in a collection are indexed--not every name. And the material has to have been cataloged and uploaded to OCLC in order to appear in Worldcat. That it not true of every item in every collection.