I located a first cousin of my ancestor in the Case Files of the Bureau of Investigation from 1908-1922 at Footnote.com.
John Fecht of Varna, Illinois, and two of his children were suspected of pro-German activity. There are three interesting pages of testimony from the agent assigned to the case. The file contains just of three pages; only the first one is reproduced here.
The unnamed daughter was a teacher and "radically pro-German." She also had "some bank account."
According to the testimony, John still had siblings in Germany, including one brother in the Army. The family at first did not appear conducive to the agent's requests, and wanted nothing to do with war bonds and had no interest in the government's involvement in the war. The agent asked several other questions and gave the father and the two adult children the night to apparently "think things over."
The next morning, the agent accompanied "them" to the bank and watched the son Anton buy war bonds. Whether "them" is all three or not is not clear.
The Case Files can be browsed at Footnote, but viewing images requires access.
Interesting...
Source information:
Suspect Name: John Fecht
Collection Title: Investigative Reports of the Bureau of Investigation 1908-1922
Publication Number: M1085
Series: Old German Files, 1909-21
Case Title: PRO GERMAN ACTIVITY
