Books
Buhk, Tobin T. The Shocking Story of Helmuth Schmidt: Michigan’s Original Lonely Hearts Killer. Charleston, SC: The History Press, 2011.
Burton, Clarence Monroe, ed. The City of Detroit, Michigan, 1701–1922 (5 volumes). Detroit, MI: S.J. Clarke Publishing, 1922.
Catlin, George. The Story of Detroit. Detroit, MI: Detroit News, 1923.
Farmer, Silas. The History of Detroit and Wayne County and Early Michigan (2 volumes). Detroit, MI: S. Farmer & Company, 1890.
Ross, Robert, and George Catlin. The Landmarks of Detroit: A History of the City. Detroit, MI: Evening News Association, 1898.
Willemse, Captain Cornelius, George James Lemmer and Jack Kofoed. Behind the Green Lights. New York: Garden City Publishing Company, 1931.
Documents
“Passport Applications,” compiled January 6, 1906—March 31, 1925. Record Group 59: General Records of the Department of State, 1763–2002. M1490, Textual Archives Services Division, National Archives and Records Administration, Washington, D.C.
State of Michigan Probate Court for the County of Oakland, Michigan. “In the Matter of the Estate of Gertrude Schmidt, a Minor.” Case file 14375.
———. “In the Matter of the Estate of Helmuth Schmidt, Deceased.” case 14376.
Ann Arbor Courier
Cincinnati Inquirer
Detroit Advertiser
Detroit Evening News
Detroit Free Press
Detroit News
Detroit Times
Detroit Tribune
Grand Rapids Herald
New York Herald
Pontiac Press Gazette
Royal Oak Tribune